The aluminum ones are 58cc as stated. Ratio will depend on more than just a flattop piston. The combo i was going to run (now for sale), was the aluminum heads, 28cc dish KB piston, Felpro race gasket (dont remember the part#) and the 383 scat crank with 5.7 rod. This put me at about 9.3 to 1.
A stock 350 with these heads will be lower, a 383 with flat tops and these heads go well into the 10.5 to 1 range---dont remember the exact number.