Why not change the gaskets yourself? Thats all you want isn't it? If you do one at a time, its pretty easy, theres no magic involved. Any local machine shop can do it if you don't want to, but it will save you some cash to do it yourself. The later Pontiac's leak at the rear main and occasionally the front seal, I never worked on the older ones, but they are similer in design.
Keep the Pontiac, there are to many 350 power trucks as it is!
If you were closer to Kansas City, I would do it for you. Dad and I have been building Pontiac's since he bought a new '55.
Joe