i have a pair of mint heads that have been cleaned and checked plus 3 or 4 good ones straight off 1700's i have broken for parts, have pistons, jugs etc as well
The only way you'll know is to take a head off and measure, the fan shroud, crankcase, V5 (and head part numbers) mean nothing.
I'm not that fussed on finding out. If the heads come off, I'll measure them. Also, think the requirement for heads has gone anyway