Which pistons?

If your desire is to keep the 273 in there for whatever reason I see nothing at all wrong with that. It's a great engine, and from what rumblefish360 said, it looks like Egge would surely be the way to go as regards pistons. Custom-built, forged pistons from any of the places I suggested are likely to cost upwards of $500.00 a set. Flat tops would probably give you the desired 10:1 compression, or thereabouts. I don't think you're going to need the pop-ups, and that fact MAY reduce the costs.

If you want hydraulic lifters, just get yourself a hydraulic grind cam (hydraulic cams are ground without the necessary "clearance ramps" that solid lifter cams have,) and a new set of hydraulic lifters, some "EOS" ZDDP-laden assembly-lube and zowie..... you have hydraulics! No more pesky valve adjustments!!!

A bone-stock 340 cam would probably work well in this engine, if you are able to keep the compression up around 10:1.

Good luck with this project; it sounds like a really neat car!!!

Bill.n Conway, Arkansas