I what kind of compression ration am I looking at with at 455 std bore, flat top pistons with valve relief if I use the 6x-8's vs the 7M5's. I only ask because the 7m5's are already in my possession and the 6x-8's would have to be purchased. Any ideas? I'm looking for a very mild build that will have nitrous. Thoughts?

Run your numbers on one of the ratio calculators. Don't forget the head gasket thickness. Felpro's run about .042-.045. And valve reliefs are 6-7cc.

Should be around 8.1.

To make it worthwhile, 9 to 9.5 is preferred to make building the motor worth the expense.

Would go with a pair of 96's or 6X-4

Thanks for the info. Looks like the 7M5's are only going to give about 7.3/7.4:1. Ordered a set of 96's from Pontiac Dude. Should give me +- 9.1:1.