I bought the wrong transmission for my 66.

So then, the car is set up for the truck transmission totally and that's what you want to leave in there. Is that right? Does your car have the correct four speed hump with the floor hole in the correct A body location? You know, I think if it was me, I would use that McCandless A body transmission. That would require a longer drive shaft though.
Well I want to remove the OD trans because it needs work done to it and I don't care for the 309 1st gear with my slant. So I picked up the McCandless trans thinking it would be an almost bolt in, except for the bearing retainer and shift rods of course. Yes if I do install this, would mean more downtime, another driveshaft, although they could reuse the ends.