72 cc E heads out of box plus an RPM cam and 3.36...

Leave block deck at .020 compression 9.94 to 1.
Mill block deck to 0...10.3 to 1

Can run safely with aluminum 1 point higher than iron heads with the accompanying performance gain.

All I am saying...is this.

By the time you modify what you have planned (heads and block)...you will have spent roughly $200 to $300 less than a ready to run set of 72 cc E heads. You will also reap the benefits of the headers you already have..plus the weight savings and have a cooler running engine, a very typical problem with Pontiac..and have maybe 30 to 40 more usable horsepower with the E heads.

I guess i'm having difficulty understanding the rationale of spending potentially $600 just to get a set of 455 heads to run at a desirable compression for a 400 not including the labor and material cost of building the heads.

Valve grind per used valve $8, SERDI valve job $200 to $250. New guides (never knurl) $100. Springs, new...to match cam $150 add locks and retainers.. $80... $550 just for basics not including labor to set up. So say $750. That's $1350 just in heads. Add the $1000 sale price of the 64's and you have your E heads.

I worked at a head/machine shop...those prices are rough as of 10 years ago. A machine shop would steer you to spend money in house over going the E head route I suggest...

I understand your goal...it's the cost/benefit ratio and your overall happiness with the end product that concerns me.