I think I know what has happened.
Stock from the factory, the block measures 9.025" from the centerline of the main bearing bore to the top of the block where the heads bolt on.
When we put together the "Stack" of parts to fill the block, we use 1/2 the crank stroke (1.740" for a 350 crank), 5.700" for the rod length and 1.560" for the compression height of the piston (the measurement from the centerline of the wrist pin to the crown of the piston just above the top compression ring.) If you add these 3 values together, 1.740", 5.700" and 1.560", you will find a stack dimension of 9.000". Now, if we fit that 9.000" stack of parts into a block deck height that measures 9.025", then we find that with the piston at top dead center, we have a space of 0.025" from the top of the piston to the top of the block where the heads bolt on. These are all standard factory dimensions, so when you add a 0.020" thickness head gasket, the distance from the top of the piston (including the gasket thickness) to the underside of the cylinder head is 0.045" (0.025" piston deck height added to the 0.020" thickness of the head gasket. This will normally work fine on a pump gas motor with iron heads that is 9.5:1 static compression ratio or less.

Problem arises when Jimmy-Jack decides he wants more cubic inches and takes the block to the machine shop to be bored and honed for larger pistons. The machine shop doesn't give 2 hoots in hell for setting the squish/quench at between 0.035" and 0.045" like Jimmy-Jack told them to. They are in business to make money and so they order up the cheapest cast pistons they can find, even though the compression height is shorter than stock (1.540" instead of 1.560"), then bore and hone the block and fit the pistons into the block. It doesn't really matter anyway, because they have built the motor to 8.5:1 static compression ratio and it would practically run on kerosene without detonating. Jimmy-Jack has no idea that the piston compression height is 0.045", which puts the squish/quench at a worthless 0.065" with the gasket thickness added to the 0.045", because he never measures it before he bolts the head on and fires the beast off.

Fast forward a few years and Mr. John Taylor comes into possession of the motor, tears it down and finds the short rebuilder piston down in the bore at 0.045".

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