[Keithc8]

The heads have the same valve spacing which is .050 wider than a 428CJ and .050 narrower than the 427 MR. The heads are the same except for the machined chambers and exhaust bolt pattern. The 428 version comes in at about 72 to 74 and the MR 427 version comes in at about 76 to 78 ccs. We check all of the heads and mill as needed to get to the desired chamber size. We order the head bare with the guides out so that we can CNC port them as needed and then install the guides. We use our own hardware as well in the heads. If you order the heads from Edelbrock they both come with a 2.09/1.66 valve package. We use a 2.19/1.75 in the blocks that are over 4.165 most all of the time. I like the 427 machined chamber because the valve is not as shrouded and flows more through out the lift range if you do the right valve job on the heads.
I would use the 6008 427 castings with the 2.09/1.66 valves in your application and they will come in at about 78ccs untouched. We do a Stage one head for 1595.00 that has our own valve job with the valves back cut, bowl blended and gasket matched and it is worth about 30 to 35 over the out of box Edelbrock heads and the Stage 2 we do is worth about 75 HP over the out of box heads. We can help you get a piston that would give you the compression that you want from a couple of companies. Good luck with your project and let us know if we can help. Thanks, Keith Craft