Which pistons?

Check with Egge Machine for cast pistons allthough their new website doesn't have part numbers listed for those pistons. I would contact them.
Another place I've found that has HP273's listed is Flatlander Racing.
Their applications offer forged pistons in standard to +.060 over in any choice of compression. They also have all other components available including Isky and Schneider solid lifter camshafts. toolmanmike