Damned parts fiches anyways.
This Yamaha 447-24510-02-00 FUEL COCK ASY 2 is used on these models and components:
1970 XS1 FUEL TANK
1971 XS1B FUEL TANK
1972 XS2 FUEL TANK
1973 TX500 FUEL TANK 1
1973 TX650 FUEL TANK
1973 TX750 FUEL TANK
1974 TX500A FUEL TANK 1
1974 TX650A FUEL TANK TX650A - XS650B
1974 TX750A FUEL TANK
1975 XS500B FUEL TANK 1
1975 XS500B FUEL TANK 2 XS500B
1975 XS650B FUEL TANK TX650A - XS650B
1976 XS500C FUEL TANK
1976 XS650C FUEL TANK XS650C
1977 XS500D FUEL TANK
1977 XS650D FUEL TANK XS650D
I don't fully trust those parts numbers that give you the models they are supposed to cross over with.