Roller Rockers 1.5 vs 1.6

Assemble everything and clay your piston tops, turn the engine over by hand, disassemble and check clay thickness.
Yeah, it's a lot of work. This way you know what you've got.

I can't remember the stuff we use at work. It's some sort of machining clay for checking tolerances like below.

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And then I suppose you can leave the head gasket out and just add the compressed thickness of the gasket to the measurement.