Art Carr can build you a 200-4R as can most good aftermarket tranny suppliers. Most 200-4R's came with the dual Chevy/BOP mounting holes. If you can get one from a 3.8 V6 car it will bolt up to the Pontiac.
A 700R4 is do-able with a $70.00 dollar adapter from Trans-Dapt or Trans-Go.
Talk to a few local hot rodders about local trans shops. If you can get one locally do that. Saves a lot on shipping and warranty issues are a short drive away...