I bet you had almost forgotten about this little task
JTC has provided me with a piston from a broken engine which I cleaned up and made was of the same class as the other pistons in the engine. The good news is that they are of the same "AB" piston type.
I cleaned the piston and weighed the piston (with rings and one gudgeon retaining ring), and then the combined assembly with rod, details as follows:
Original 422g + 943g = 1365g
Replacement 424g + 942g = 1366g
When I do replacement piston + old rod the answer becomes 424g + 943g = 1367g
That's good enough for me at the moment
, and it indicates that the original piston has lost 1-2g of material onto the bore walls. Time for some evidence:
I haven't worked out what the discolouration marks are yet on the replacement piston