I've had a couple 8" rears with factory 3.25 gears, not real common but out there. With the five speed a lower ratio would be preferable for drive-ability. A 3.55 would be even better. Since the 8" is common to the popular Mustang and even Falcon/Comet crowd parts are still plentiful.

One comment on the Camaro derived T5, you may already know, they are designed to be rotated, I think something like 17 degrees so use an unusual bell housing and the tail shaft housing would have a canted rear mount if you tried to set it up in "conventional" manner. Also, relative to placement in a model A the shifter (also canted) would end up under the seat, or well back with buckets.

WC T5s can take 300 ft. lb. pretty well, so watch the torque rating of the engine, not just hp