Early stock heads like a X or J head or older W2’s.
For power, if you have the coin, go W2.
The stock heads, as cast, do not support much power even on stock displacements. Porting a stock head quickly escalates in money to aluminum head money.
You could still do very well with a stock head. Though it’s choking the engine @ 400+ cubes.
Reading, “a street engine that never see’s the high side of 5500”, a lot of power can still be made down low.
I don’t think it’s considered open chamber but the 65cc version of the small block head has room in the chamber to clear stock high compression 340 pistons which are .025”-.030” above the deck. I think they are PN 60175.
