Using the math for my 517 using 75cc chambers, I've come up with ~11.48:1 with 10 cc's for the gasket, 4 for eyebrows and 12 in the dish.

Gary, That's about the range I was looking for, 270 @.400, 345-350 by .650 is where I want to be. I'm actually looking at doing a -1 with some epoxy fill in the floor.