To the person marking halves and re-aligning them upon reassembly: old alignment doesn't matter nearly as much as torquing to the right spec. Pop pressure is not so much preserved by the closeness of original shell alignment, but by the spring + shim length w.r.t. inside chamber length.

As people mentioned, when you lap halves you shorten the (internal) spring chamber length, which has the effect of raising pop pressure.

And when you lap halves, any alignment marks made on the two halves are immediately rendered even more meaningless.

Torque to spec, check pop pressure, and adjust shims accordingly, repeat until spec pop is reached. Or, just slap 'em back together and hope they're better than before and if they are, great!

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Cheers!
Scott McPhee

1987 300D