Charely
There are 10 and half dozen ways to build a Pontiac, but to think you won't go fast in it... that is a huge mistake. The majority of stock components adjust the compression with head cc and gasket crush. I believe you have a SD, if memory serves me correct. You will probably want to stick with the factory heads. TRW (Seal Power or whoever they are now) did make a shelf piston for those rods, it only had two valve reliefs. If you find some nice .015 crush gaskets, run a zero deck, and mill the heads accordingly to achieve your final compression ratio.... I think you will be happy. Running low 12's with a 9.5 455, is a piece of cake and you get to use pump gas. Then again maybe you will want a highway cruiser. Some of the old cross country racers use to order these SD's with the highway gears, and achieve some serious cruising speeds.
Steve