Will a C4 from a '78 Ford truck work in a '66 Coupe?

 

I believe the input and output shaft splines are different (24 vs. 26 spline), and bell housing is different. Do a search on the web "input shaft C4".

 

No only that, the FLAIR case C-4 torque converter has a 11 7/16" bolt circle and the car STEP case has a 10.5" bolt circle. The dipstick in the pan won't be hard to convert or bend but you'll need a new flexplate to do it also.