Piston identification

Hi, I have a problem identifying my piston. The bike is a 91' KX250 and it has a steel sleeve in it and I'm positive its been overbored from stock size. The piston doesn't appear to be forged so that takes wiseco off my list, but all it says on top is "73.95 MM" (the size of the piston diameter) in the center of the dome, and on the rim of the dome directly above it it says "J19A4". There is another number that is also in the center of the piston dome but I buffed off half of it while taking off the carbon. It's directly above where it says "73.95 MM" and I can only make out the first and last of the four digits, they say "8 - - 5". Between the 8 and the five, the two unidentifiable digits seem to be 0's or 9's if that helps. If you guys could help me out or guve me any tell tale signs of any piston manufacturer I would love it. I need to know in order to buy new rings for it. Thanks a BUNCH!

Anyone?

What is the normal stock bore of a cylinder? This is the first top end of the bike since I've had it and I don't know much about the history, what could this "oversize" piston indicate? Can I go any bigger or what? The cylinder has been sleeved, if that helps? Should I look for anything else while its apart?

WOW! Is that bad or anything? I guess it explains why my friends tell me my bike is so powerful. Can anything bad come from this overbore? Thanks.

I can get pictures from my digital camera, but I have never been able to post them up here on DRN. If anybody wants to try for me I can e-mail the pics to them. Just what would you want pictures of anyway, the piston, the bore, etc?