The deck bridge/depth mic will also get it there as it will precisely show where the piston height maxes out. It won't show exact TDC because there are (at least) a few degrees of crank rotation where the piston dwells at the top of its stroke but for this kind of measurement it's the easiest and most straightforward method, IMO
Is there a way for a machinist to accurately measure and correct deck height without the machine/fixture for square decking, or without installing pistons and rods and checking where they sit at TDC? I'm imagining a set of big calipers going from the main bearing bore up to the deck but I feel like that wouldn't be very reliable...