I would go with a built 200-4R, with a lockup convertor. THe 200 fits in the same space as a Turbo 350, while the 700R4 requires a shorter drive shaft and you also will need to move the trans cross member back. On my 65 Chevelle I also had to beat the trans tunnel to get the 700R4 to fit.
You can wire the lock-up convertor to turn on with a switch, and have it kick off from the brake switch. Yank makes a nice lock-up convertor that can handle torque.
JMHO
-Sam