The chamber must be created in the piston dome to have quench and turbulence.
It's not a big problem, but it requires a fairly tall compression distance and a heavy piston. The stock 302 height is probably OK but any stroker or long rod will have to be done carefully.
The minimum depth of the cup (negative dome) is close to the lift near TDC for both valves + safety margin (look at the cam data), the area roughly a triangle circumscribing the seats and spark plug, and both made larger until you have the volume you need for the static CR you want. In a 302, 9:1 is 6.3" or 103cc, 12:1 is 4.6" or 75cc. If you have the room (low CR) the exhaust side of the cup should be deeper.
The chamber outline should tend to extend out more on the side facing away from the port.
