Madscientist needs to think outside the box.
Here's an example: The goal is to have 0.040" clearance between the piston top and the "squish" area of the closed chamber heads. If one adds all the numbers, it becomes obvious that with stock dimensions the high compression pistons end up sticking out of the block 0.018".
Now to get the desired clearance one needs a gasket with thickness 0.040" + 0.018" or 0.058". Send money to Cometic or scour the Fel-Pro catalogs, etc.
ANOTHER way to do it would be to mock up the block and measure how far the pistons actually stood out of the squared-off deck. The pistons would then be cut down the desired amount to get the surface of the "squish" area to zero deck. This would leave part of the piston still standing out of the deck.
The problem with buying the so-called "340 style" open chamber heads is that one is forever stuck with the squish area eliminated. Now if building a stroker engine, a custom piston shape is required to regain the mixture motion that the squish area would have supplied. On the other hand, the closed chamber head may require some material removal on the piston top to provide a desired compression ratio, but it is easier to remove material from a piston than to add it.
R.
Dog, you are making it way too complicated.
If the head is OC (and I have flowed both open and closed...it took many hours and lots of tests to get that stupid W-5 chamber in shape and I had to use an odd ball valve grind to make it right so just because it's closed chamber don't make it right)all you need to do is finalize CC size, meausre whay you have left of the open side (I try to keep it at .090 or so) and then add the gasket and do SIMPLE math. Lets see how it adds up:
Chamber depth (approximate..must be measured) .090
Gasket thickness (typical) .039
Equals .129
Minus deck clearance .040
Equals .089
That means to get .040 quench with these numbers the piston must be OUT OF THE DECK .089, and if you don't want the piston up that high, you can mill another .020 off the head and use a .027 gasket and you would be out less.
Obviously increasing the stroke changes things but the math is still the same. Those SP pistions you have are just like a factory 340 piston. Most 340's had an actual compression of about 9.8-9.8:1 from the factory.
And like someone else said, .040 quench is not that big of a deal when using Chrysler heads. For a production chevy, with a junk chamber and a bad spark plug location it's much more critical.
