mystery number on honda piston

[1984 honda 200s]

Hi guys, ive just bought a decent honda 200m engine from a buddy of mine. He says it ran fine, no smoke.
Welded on shifter and broken studds in the head.... so i tore it appart thismorning to find out that im sure it isnt stock..
Ive found the cylinder to be perfect and the piston to be clean aswell. But there is a number 50 on the top of the piston, does this mean its bored .50 over stock?
The piston is OEM it says honda on the side of it and its a bowl shaped, not flat..
Otherwise i put one of my other cylinder heads on it fresh valves and seals, runs awsome tones of compression no smoke,.

[hoosierlogger]

Yup .50 overbore