Putting a C4 in would make the car fairly useless as a highway driver. It would be spinning around 3000-3200 at 70ish mph. As a drag car, the C4 would be better, but as a street driver, you'd be better off getting a properly mod'd AOD, upgrading to an AOD-E or 4R70W or a M5R2 swap.
Physically, any trans that fits a 302 block would bolt to a 3.8. The bell housing is the same. Finding a starter, flywheel, cluthc, convertor, shifter, kickdown cable, driveshaft etc to fit other trans models will be a little time consuming and expensive. People have fit T5s and T56s in, but it's not a 'go buy parts and put it in' swap.
If you can't do massive fabrication yourself, stick with the AOD or you'll be sorry later.