[Mgb-v8] Thrust face of a piston

[Smit, Theo]

It's the side that is opposite to where the crank throw is on the power
stroke. Visualize what the angled connecting rod is doing, and it's easy
to determine which side should be taking the load.

If you disassemble the engine it should be pretty obvious also... One
side of the piston (and bore) will wear significantly more than the
other.
Cheers,
Theo