I would seriously look into replacing the MC instead of rebuilding it. At that age there is likely to be some pitting and rebuilding it is probably going to be a waste of time. Go to a real parts store and they may even have one in stock. A lot of these older cars parts like that were used for years AND in other makes and models. I don't know about yours, but they had one in stock at the local parts store for my 59 Rambler, that and the wheel cylinders! And this is NOT a "classic" auto parts store, we are talking just a good old REAL parts store that services the shops in town.