Hi 52,
I'm afraid its a "no". The 216/235/261 bellhousing is different from the later 250 bellhousing. No modern standard or auto tranny will fit a 216/235/261. There are adapter plates available, but I've heard of several of them cracking. Does your truck have a torque tube? If so, you'd have to swap the rear axle to use a later tranny, and have a custom driveshaft made. You'd also have to buy/build a custom tranny mount.
Swap in a 235 with an old Hydramatic or a 3 or 4 speed (235 era) standard tranny. Otherwise, go ahead with the V8, cuz the work to put a V8 or any later I-6 would be about the same.
chip
