GPZ 1100 B2 cylinder size question??

I'm in process of restauration of GPZ 1100B2 82'.
When I opened engine there is engraved No. 50 on all pistons, it's propably overbored but when comparing with my friends pistons( wich he claim it's stock, in his possesion for last 25 years(well now it's blown) from same GPZ 1100 model he also have 50 stamped on all pistons...measuring cylinders give me a size of 73mm( stock claimed by Kawasaki was 72,5mm). Comparing with part numbers there is no size mentioned for piston rings only letters :
1. SKU: 13024-5023 RING-SET PISTON LL
2. SKU: 13025-5019 RING-SET PISTON L,O/S

so wich ones are for 73mm barrels and 50 marked pistons???? is 73mm first over stock or second, is factory recomendation to increase cylinders by 0,25 or 0,50 when reboring is needed.

Thanks guys

Buy the way I have extra :pardon: standard piston rings 4sets ordered wrongly anyone interested??
SKU: 13008-5037 RING-SET-PISTON,STD 4 sets

I believe a "0.50" means that it is 0.50mm over sized piston. I bought some 0.25 mm over pistons for my 750 and they do have "0.25" stamped on top. FYI, Kawi only supplies 0.50 over and 1.00mm over for mine but aftermarket has sizes in 0.25mm increments over up to 1.00mm over. So, on my 750 twin, first over from Kawi is +0.5mm but first over with aftermarket pistons is +0.25mm. Very confusing.

That is first size over, .5mm