how to find the correct front master cylinder rebuild kit

[DuWizard]

got a problem, have a 68 ironhead bobber, the front master cylinder was one that was laying in the shop ( no idea what it came off of ) and put on the bike, worked good for 3 years now leaking, need a rebuild, no one wants to do it here, and i cant figure out which rebuild kit to order, am i doomed to buy a new cylinder??

[goldstar]

I noticed a person in your city, on a motorcycle site, that also has a 68 ironhead. Maybe find that person and compare notes.
If the master cylinder make and model cannot be determined, I would not attempt to guess fit parts. I do the work, the brake fails and you wreck, I'm sued.
Buy a new one.