There's a piston for Holden engine that a 273 can be bored too but it haves a Chevy pin so you have to run Chevy 6.125 rods and with a 360 crank puts just about zero deck, but if I was gonna do it I go custom pistons, Done right you build a super fuel efficient 300ish HP engine and custom aren't that much more than good off the shelf piston they want $700 for KB's for my 318.