Sealed power H621P

FMECat.com will give you the listed specifications but the volume is not listed.
I checked the last printed catalog from 2005 and it does not list the Volume for that part number.. I will see if I can get it if you are not in a hurry.

Steve,
You better tell us what you are up to with the pistons!!

It's a 92 prostar / 351W / GT40 heads / powerslot / ~1400 hrs

There are hairline cracks in the waterjacket of the head.   Plugs were very rusty when purchased last fall, this set was new this spring.   So the leak has been there for a while, and while I haven't seen any water, rust on new plugs suggest it has been actively leaking this summer. No water in oil. No water on plugs tips.

Engine is out. Internals were very clean. Block is off to machine shop.

Will use
GT-40P heads
Cam research cam (0.490In/0.490Ex/218In-222Ex@0.050/112LSA)
H621P pistons
Stock intake / exhaust
Undecided on distributor

The H621P is a Hypereutectic piston, have your machine shop bore it to the bore size shown on the piston box. IE: 4.030 for a 30 over. These pistons don't grow as much as a standard cast or a Forged Piston so they do not need more clearance added as many machine shops will want to do for you. They will offer better fit which gives better ring seal and if you increase the bore size beyond what the oversize is you will give some of that advantage away. The factory builds the clearance needed into the piston and gives you the needed block size on the part number outside the box.   If you plan to add Nitros, a Turbo or a Supercharger you may wish to add extra clearance to your bores.