I have a 73 440 I'm going to install some 440 Source heads on. It has a stock rebuild from the previous owner using the original pistons. I know these were low compression (anybody know what it was?). My concern is the original gasket was .020 thickness while the one I'm going to install is .039 crush depth, further lowering the compression. I'd like to actually increase the compression over the stock numbers. Something around 8.5 or 9:1. It appears the cc of the new heads is close to the stock ones. Can anybody recommend how much to mill the new heads to achieve this ratio? Plus the Performer RPM intake will need to milled too to fit properly. Need the numbers for that too. Thanks