I have a '79 F-250 4x4 with a 351M, C6, and NP205. I am swapping in a 390 and already have another C6 from a 2-wd truck. I measured the transmission to transfer case adapter and the spline depth in a NP205 and after figuring came up with about 8" total for tailshaft length on a 4x4 C-6. I measured the 2wd tailshaft housing and came up with about 8" for tailshaft length on it also. If I remove the tailshaft housing from the 2wd tranny, can i use it in my 4x4? Has anyone done this swap?

 

No it won't work, you'll have to swap the tail shafts.

 

I just finished this swap, and you'll have to swap the tail shaft and housing. There are 3 length's of the tail shaft's and housing's, make sure you get the correct one for your truck. The rear tail shaft is held in by a snap ring, so the transmission will have to be taken apart to swap the tail shaft.