[Master Cylinder, again]

Help, Again. I thought I posted yesterday, but I don't see it. Anyway, I have a'63 Avanti and the master cylinder went out this winter. It is a dual chanber one with the following #'s on it: 8515B and 7188V, and no other markings. It does not cross reference with anything! I ordered what I thought would be the exact replacement (the "Fruit Jar"), but I'm concerned that it won't work. Does anyone have a suggestion? Many thanks, Spencer