According to the P.O. of my '66, the transmission has problems and that is why he parked it for over 10 years. Anyway, I just got it running again and was wondering if I should bother trying to get it fixed or swap it out for something else. I guess a C6 would be the way to go if I am swapping(although I have an FMX lying around). Would I have to drill any holes in the frame to remount the trans crossmemberor is it a direct swap?

 

I believe the C6 is a direct swap as long as it's from a truck. Definitely go with the C6, not the FMX. Even a car C6 will work, you may just have to play with driveshaft, linkage etc. I have a 68 F100 that I'm parting out which has the same type flange on tranny output, however the 74 F100 I just parted uses a slip yoke. I have three C6 FE cases, all of which are maimed in some way. 1 has hole in side of bellhousing (still works fine), the other two each have 1 bolt hole broken on the bellhousing. I'm still looking for a good case.

 

Any FE C6 will fit any FE engine.
There are 2 types of C6 found in the trucks '65 - '76.
One has a long tailshaft housing with a slip yoke for the output shaft. This one uses a single piece driveshaft, and can be found in both long bed and short bed setups.

The other has a short tailshaft with a U-joint output shaft. This setup requires a two-piece driveshaft with a slip joint and carrier bearing in the middle. This one is usually found in long bed models.

Either will bolt up fine to the stock transmission cross member, which will bolt up to the same stock mounting holes '65 - '79.

It is easier to convert from a two piece driveshaft to a single slipjoint one, than the other way around.

If you use a car transmission, though, you will find shifting difficulties. The car's input shifter shaft on the side of the transmission is not positioned the same as a truck's. You'll need to swap out the shifter shaft for one from just about any C6 that was in a truck. If you stick with the car shifter, you won't be able to get it into Low, possibly not into 2nd. It is very easy to swap out, though. No special tools. Remove the pan, filter and valve body, then unscrew the large retaining nut on the shaft, and slide it out. Change the little O-ring while you are at it. (Note - You will also need to do this for any truck C6 made later, as the shaft for the '80s trucks has the same design as the ones made for the cars in the '70s. I used an '83 C6 when I put it in my 66 behind a 460, and used the internal shifter shaft from a '78 C6 that came off a 302. Of course, you won't an FE C-6 after '76.)

Finally, you will find the shifting linkage between the steering column and the transmission to be all out of kilter. The '65 - '66 uses a threaded shift rod that threads up at the steering column, with a small pop-in at the bottom onto the internal shift lever.
The '68 and later ( I think '68, I may be off a year or three here) use a pop-in up at the steering column, with a slip fitting at the bottom on the transmission's internal shift lever.
I found it easier to use a '72 automatic steering column in my '66 than try to finagle it all together.

Also, you will probably need to add a transmission cooler, and the cooling lines will need to be re-routed. The COM uses a side-mounted water cooler, most likely. The setups can vary, but you may need to plug a fitting in the block and re-route a radiator hose as well.

To answer your question if this is a bolt up swap, you must answer the following questions:
1. Is the output shaft the same for both? If doesn't matter if the U-joints aren't the same size; you can easily get conversion joints.
If the answer is no, then no, it is not a bolt in swap. An FE C6 will bolt up to the engine, but you will have to make driveshaft modifications in addition to what I mentioned above.
2. If the answer to this question is yes, then ask the following: Is the COM transmission you have in there now the same length as the C-6?
To answer this question, measure the distance from the bell housing where it mates to the engine to the output shaft. It they are the same, you can substitute the C6 for the COM and use your existing driveshaft setup. If not, you wil have to make driveshaft adjustments.

Hope this helps!

 

Thanks for the info, that should help quite a bit. I have a long bed with a 2-piece drive shaft. Any idea what year C6 would be the same length as the C-O-M?

 

the c-6 is a different length. the back shaft will work but you will need a different front half. be sure to get both balanced together or they won't make 6 months. been there done that "short cut"

 

Like I said earlier, my 68 F100 has the C6 with the same style yoke as the Cruise-O and it appears to be the same length. My 74 does not. My thinking would be 68-72 would be the ideal but I'm not positive on that. I also have a 72 F100 LWB at my Dad's house in Oregon and I believe it also has the yoke like our 66's Cruise-O. That truck is a 360/C6. My 66 has the two-piece driveshaft that bolts to the trans just like yours but I would rather use the slip yoke at the tranny style because I want to go to a 1-piece shaft. Good luck with the swap.