I finally got the C channel. It used to be 4x2 square tubing but they cut one side off. All the C channel I coud find was 4 height x 1 1/2 flange. What would be the best way to weld it onto the frame? This is with an arc welder.

 

Aren't you just replacing the stubs behind the rear spring hangers that were torched off to install the hoist? If so, I'm guessing that you just want them back on for bed and bumper mounting. If that's the case, then the stubs and the welds won't be bearing any load to speak of. I personally would have lopped the sections you need off of the parts truck chassis so that it would all be the same high carbon steel, but for what you are trying to achieve here, this plan with mild steel C channel should work just fine. Use 7018 welding rod and weld all the way around it. It wouldn't hurt to leave a small 1/16th inch or so gap between the rails and the patches. Grind the welds on the outboard sides only flush and them weld a diamond shaped fish plate over the seam to reinforce it that will overlap the seam on both sides by 2-3 inches. If you are not an experienced arc welder, have somebody do it who is. The vertical up welds on the sides take a knowledgable hand or lots of practice in advance.

 

I gonna have my dad weld it. I thought of using the rear section of the other frame. Since it's a F-1 it is exactly the same length as it is now. We are gonna tilt the frame so it is easier to weld.