G’day. I’m building a 273 over here with this sort of thing in mind. 360 crank, 253 Holden pistons, 300ci. 400ft/lbs-430 should be doable. Airspeed/compression/V/E and a small cam is how we’re going to do it.Getting the engine stroke/bore “square” is another thing. Very confident in getting 350hp/420ftlbs atm. 273’s are a “torque” engine ( ask Richard Ehrenberg), valves are too shrouded by the bore, gotta make the little thing efficient.