I always wondered how you do this on an 8v with hydraulic tappets!
By the piston through the plug hole when it hits TDC? Because you can measure the lobes as they are sealed in.
no race engine would be built using hydraulic tappets so wouldn't be an issue
but your right, a probe down the plug hole will help find tdc.
think i'm right in saying (maybe sputnik or fruity will confirm) but you don't actually try and find tdc itself by using a dial gauge and finding the highest point the piston rises to as there is a point where the piston remains stable but the crank can actually still turn by a fraction so it's not the accurate way of finding true tdc.
the way i think
it's done is to find a point where the piston is before
tdc, say 20mm before (the figure doesn't matter, just needs to be a point on the dial gauge) the piston gets to its' max height and mark that point on the flywheel/angle card.
you then rotate the crank until the same point of piston travel is met after
tdc, then mark that point on the flywheel/card.
split the distance between the 2 marks and that is the true tdc.