[David]

I recommend laying a piece of solder across the piston held in place with some Curil-T then bolt on the head. Make sure the solder length is the same as the bore so it reaches all the way to the edge of the squish area. Turn the engine over and then disassemble. Check the thickness at the two ends of the solder. There's such a tight area at the edge of the piston it's really hard to measure with just a depth measurement off the top of the cylinder.

I should be getting my new 3.4, 7.7:1 JE pistons tomorrow and will be doing this all over again. I'm shooting for 0.035".