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You didn't have the piston at top dead center. The measurement should be somewhere between zero and 0.045". What's with the mm? Get a set of feeler gauges that reads in thousandths of an inch. Wadda...

This measurment exercise assumes that you don't own an 8" dial caliper.
With the motor on a stand, tilt it so that one bank is level. Using a steel rule and a set of feeler gauges, we'll find the...

What kind of power number are you looking for?

By the way, If the heads aren't on the motor yet, then you have a golden opportunity to measure the piston deck height.

Have you bolted the heads to the short block yet?

They are for 3/8" studs. You have 7/16" studs in the heads. Or at least that would be my best guess.

Here's what you need to convey to us:
Piston deck height.
Compressed gasket thickness.
Chamber volume.
Piston part number or description of the crown configuration.

If you don't know how to...

The rockers should be stamped with the ratio. Check that first. Then see if the nut fits down in the rocker. Then see if the rocker trunnion fits the stud. You said the nut won't fit the stud. Is the...