I'm fairly sure it was YB125 (not 100) or the older YA6 125. (YB125 superceded YA6) I have the correct part nos somewhere from a guy in NSW who used to do the conversion & probably still does. Its all been posted on here before
Stepped pin on older bikes has same big-end dia as later models I'm told. As far as I know, all Ossas used same rod, even the 350, but I could be wrong
But I'd have tho't the Ossaworld kit would be as good.
Yam conversion needs machining of the flywheels cos bigend bearing is wider than the Ossa's, which means you lose some of the flywheels' 'grip' on the big end pin. Its not a straight swap-over