Here's some information I have that might help. This particular installation was for a 1955 but I would imagine a 56 would be very similar. There were some pictures that went with this but I guess they were lost somewhere. The "Briggs" referred to here is the guy doing the work...
1. Place a long piece of angle iron 2 3/8 inches behind the centerline of the hole in the forward body-mounting bracket. Make sure the iron is at the same position on both sides of the frame. This will provide a good reference point and will retain the stock width between the framerails after you remove the front-end. Place a good tack-weld on both framerails to ensure that everything stays put when you do the cutting.
2. Locate the centerline of the truck's straight-axle by measuring 28 3/8 inches forward of the reference brace. On '53-'56 Ford F-100 models the axle center is 27 inches forward of the center of the body mounting holes.
3. Secure the frame in the jig and check for the proper ride height. For a good slammed stance, set the lower edge of the framerail at the centerline of the stock axle at 11 inches off the ground or, in this case, at the bottom of the frame jig. Next measure the ride height farther back on the rails at the horizontal area just before the frame starts its rise over the rear axle. There should be 12 to 12 ½ inches between the underside of the frame and the ground. The measurement at the back of the frame should be 16 to 16 ½ inches from the underside of the frame to the ground.
4. In the front of the car, the underside of the front crossmember/core support should be about 9 inches from the ground. Jackstands can be used. Briggs worked on a bare frame taking measurements to the bottom of the frame jig.
5. Hold the tape measure on the cross-brace /reference point and measure forward to the middle rivet that holds the crossmember to the framerail. Record this measurement to use as a reference when you reattach the front portion of the frame later. Measurements of this area and the lower center of the crossmemeber are very critical and must be accurate.
6. Measure 14 inches back from the predetermined centerline of the axle. Use a square to mark the rails across, down and on the underside. This is where the first cut will be made on the truck rails.
7. Briggs used a plasma cutter here. But cutting torch or a sawzall will work. Try to hold as close to the line as possible to keep the cleanup grinding to a minimum.
8. You marked off the section of the frame to be removed for the swap in Step 6. You can cut it at this time.
9. Cut both framerails and set the front section aside (this front portion will be needed later). Grind the cuts smooth and clean the area near the cuts to leave a good surface for welding.
10. Checking the two frame sections at the mating area indicates that the Camaro frame measures 37 inches across from the outside of the rails. The early F-100 frame measure 34 inches across from the outside of the rails and must be figured in when you set up the two later.
11. Set the '78 Camaro clip on the jackstands and level up the flat area at the rear where it was bolted to the floor of the Camaro. To locate the centerline of the Camaro axle place a level on the flat area of the side rail and measure to the center of the ball join on the lower A-arm.
12. Use the measurement from Step 11 to the top of the frame. That works out to be ¾ inch forward of the mounting hole for the shock absorbers. This becomes the guide mark for the swap.
13. The first cut on the Camaro clip will be 14 inches back from the centerline of the axle. That's just behind the rear mounting bracket of the lower A-arm. Be sure to stay clear of the bracket or adjust the measurement to clear it. Use a level to mark the vertical lines to ensure that every cut matches up.
14. Use a plasma cutter or a cutting torch to cut the frame. It helps to turn the unit over so a clean, straight cut can be performed. This cut will be a butt joint with the truck rails, so it is important to make a clean, straight cut.
15. Set the Camaro slip into place with the top of both frame sections matching up. To ensure a proper setup use a degree finder on the bracket of the upper A-arm. Set the section to a reading of 10 degrees at the rear sloping angle.
16. Check the centerline of the axle and make sure that it measures 28 3/8 inches from the crossbrace. That is the same measurement that you took on the centerline of the truck axle. Hold to this measurement.
17. Double-check everything and tack-weld the two sections together at the top, the bottom and a couple of spots on the sides.
18. The front portion of the Camaro clip must be cut off to allow for the reattachment of the forward section of the truck. The Camaro frame should be cut off 1 inch in front of the upper mounting hole of the steering box.
19. Cut off the front section of the Camaro framerails and set the front portion of the truck frame into place. It is important that both bottom surfaces are aligned. The front section should measure 50 inches to the middle rivet holding the crossmember. The center of the crossmemeber must be set at the same measurement as its stock configuration.
20. Set the steering box into its mounting location to make sure there is clearance with the crossmember before you weld this section into place.
21. The Camaro framerails are quite a bit wider than the truck rails. Trim off the outside section so you can fabricate boxing places for the better alignment of the two sections.
22. First make cardboard patterns to determine the proper shape for the plates. After you bend up the plates, tack-weld them into place. Briggs cut his plates from 3/16-inch steel sheet.
23. The width at the back of the Camaro Framerail has to be narrowed about 1 ½ inches. Make an angular cut starting about 3 inches forward of the joint. Then remove a pie-shaped cut from the lower side rail of the truck frame to mate the frame with the lower edge of the Camaro unit.
24. Again make boxing-plate templates from cardboard to ensure you have the proper shapes before cutting plates out of the 3/16-inch steel sheet.
25. At this point everything should look good, but it's still only tacked together. Check all of the measurements again to be absolutely sure that all areas are correct.
26. For a true check of the ground height at the spindle, set the upper A-arm and the spindle and raise the lower A-arm with a pipe on the floor jack so the lower A-arm is parallel with the ground The axle should be right at 12 inches.
27. After you've welded everything up and ground it smooth you can reinstall the painted suspension parts. First work the lower A-arm into the mounting brackets.
28. Next install the upper A-arms, the sway bar and the spindles. All that remains now is installing the brakes, the springs and the shocks, and the swap will be complete. When installing the coil springs use a good spring compressor and work carefully as this is a very critical part of the job. The installation can be dangerous if not done properly.
Hope this is of some help!