Another item to be VERY careful about. If you buy a 10 1/2 to 1 302 piston you will get about 11.9 to 1 with the 393 stroke. You may wish to start with a 9 to 1 302 piston and calculate your compression ratio very carefully after you find the volumn of your combustion chamber and the thickness of your head gasket. Been there done that, screwed it up, still got lucky!
h dog