I'm putting a Super T-10 where a T-350 is now, into a '66 Elco.

Can you give me the lowdown on what yoke to use on the driveshaft? I don't remember the number of splines of the 2 trans types.

Do you happen to know if the driveshaft length will need to be altered in this chassis /trans combo?

I'm not sure, but I think the TH350 has a 27 spline yoke and the Super T 10 has a 31 spline yoke. I may be wrong on that. The drive shaft length should be the same, but it will depend on the length of the yoke.