[arocars]

A 200R4 swap requires a new torque converter, dip stick, TV cable, adapter on the carb, crossmember, shifter alteration (to get all 4 gears) and potentially a shorter driveshaft. I did a T350 to 200R4 swap on my 69 Camaro. It cost $2k in parts. I created a custom crossmember. *** It was not worth it. I didn't drive the car often enough that I needed the overdrive.

The T350 has a deep first gear, so that would be an advantage over your 4 speed. But both the T350 and whatever 4 speed you have will both have the same 1:1 final drive ratio.

I have a sbc 350 and T350 in my 68 truck. I haven't actually checked, but I would guess it has 3.73:1 gears. I dont drive the truck enough that I care about gas mileage. So, I would not put an overdrive in it.

If you have 3.73:1 gears, your truck should not feel heavy and slow in 4th.

Too bad you're not closer. I would swap all my T350 stuff for all your 4 speed stuff.