Every advice I read and discussed by PM from capable engine guys is to deck the block. I understand not wanting to grind down 20 thou on a numbers matching stock block. That's why a mentioned perhaps moving the piston top up with a custom piston instead of grinding the block down. Custom rod will do that too, but I figure the piston will need dishing for a lower CC head anyway, for pump gas. Especially after I just bumped cr up a bit by decking the motor. A custom piston will do this all in one purchase. The $500 Ross custom piston will be lost in the total expense. At the same time, the custom piston can be dished to lower CR a bit, depending on the head. I'm not sure how that effects quench and detonation. I have not found much discussion about that.

I guess my problem is a bit different. I have a 71 GTO motor with '96 heads. I need more compression not less and I don't mind milling zero deck or reducing the chamber volume on the heads to get to the sweet spot. My motor doesn't numbers match anything now.

Saying the original engine wasn't decked from the factory and ran fine with original pistons back in the day doesn't address the concerns of todays octane fuels. Lets remember that the stock block didn't and couldn't run decent on today's pump gas. My 350 I had in 1968 required Sunoco 230. I ran many tanks through above and below 230 and that was the best choice. Otherwise it pinged. Or a grade higher I paid $2.60 instead of $2.45 to fill the tank. My mom's '67 Olds 88 350 Rocket had to have Sunoco 260. Without 260, it could drive for miles around town with the ignition off.

Zero decking helps reduce detonation by permitting less advance for the same sweet spot on power. It reduces heat also. Since what isn't heat is more output, you get more power. I think zero decking is just about a given for a rebuild on a car one wants to drive. The question is my mind is to do it in the pistons (more cost) or machine the block (damage no's matching block). Since you can make new pistons but can't replace metal on an original Pontiac block, I would tinker with the pistons.
In other words, I would consider having the block decked flat and no more. Perhaps the machine shop will come back with advice the engine is adequately true without any milling. I read Mr P-body of Central Machine, Va saying align bore should not be routine, but rather the engine checked to see if it really needs it. That flys against notion of blueprint everything, grind it to spec and make it all new, but grinding stuff down isn't renewing, it's refurbishing, right? Anyway, then knowing what brought the engine true at the machine shop, define the pistons and have them made to suit.

I think the second half of the issue is to get down between 9.2 and 9.5 compression ratio (assuming iron heads). Then you can enjoy the car on pump gas and not trailor it around or baby it or need to feather the throttle because marbles are bouncing around under the hood. You then don't need to be within a hundred miles of racing fuel and your home mixing gas containers. To me, that is what the car is about. Driving the car, WOT at times, no worries and filling up on pump gas where you find it is the win.

To me, the ideal is to run on pump gas and enjoy the car. And pump gas is a loose term that I think will deteriorate even more in the next ten years. Newer cars run on 89. Eventually that will be what you can buy.

If a 400 won't produce the desired power at 9.2-9.5 CR, then its time to stroke it with an eagle crank or a turned 455 crank. I know it's not no's matching stuff, but if you don't grind down your engine and don't throw away the original crank, you have a path back to originality. That is what I see as most important... to not throw away history. So I don't see that ross piston or different crank as horribly important because it's out of view. At least not when driving and enjoying the car is at stake. I think that custom pistons and even an Eagle crank is better than closing the hood at car shows because you're wearing aluminum aftermarket heads. It's better than milling off metal you can't put back too. Aluminum heads let you run more compression, but they just don't look right on a restoration. A ported iron head or port matched intake isn't strictly no's match, right? It looks right, but it's an improvement at least from many peoples viewpoint. I guess with my faulty reasoning, you could say store the iron head and install the E heads and move on. Or even store it all and run Cheby box stuff. I guess we all have lines drawn in the sand. Life is full of compromise. We all have tough decisions. Trade off is between totally original and drivable and how to get there? If you buy Sunoco 230, all the original stuff will work perfect when it's up to spec.