If the goal is to keep the drivetrain original. you may want to source a standard 326 or 350 V8 with a 2 barrel carb and factory cam. Of course if a higher output engine is used, then other drivetrain components will require an upgrade.
I often look for Pontiac engines in my area and find it funny when they're listed as a "big-block" Pontiac. There is no such thing, Pontiac blocks are all the same size.
