Couple of questions first.
Do you intend to keep the car origonal?? Like with the 6 cyl? Do you intend to take it on Interstate Hwys much??
I'm asking to see if your a candidate for an overdrive tranny. Modernizing your car is the thing to do, not always the answer for everyone though.
If your a candidate for an OD trans, spending money twice(fix-later replace) isn't the best.
If I'm reading correctly you alreay have a V-8 in the car, you have prolly gotten the use out of the 6 cyl C-4 in that case. Time for a replacement trans.
My reccommendation is to get either a T-5 five speed manual or a 4R70W automatic. Some folks say an AOD is the easiest automatic to use, I heartily disagree. Before getting into that, plz let us know more bout what you have and intended uses.

Tubo

Well far be it, from me to argue against what someone chooses to do with their own car.
I will stick with, if you have a 6 cyl C-4 bolted to a V-8. And the C-4 is slipping. Ya prolly  need to replace it.

Tubo

Thanks Guys, Yes I'll remove and install it myself, I feel confident I can do that. Anyone know if the 67 c-4 is a drop in replacement? Beside that fact that I don't think a 67 is a green dot.