proportioning valve questions

[GTA350VORTEC]

Im currently working on a 75 firebird 350 4bl and need a new proportioning valve, however when Ive searched places like classic industries and year one it seems they only sell valves for up to 74, can I use this valve in a 75? It looks the same. The car has front disc and rear drums. I know this is a 3rd gen board, but Im hoping somebody knows about the 2nd gens here too!! Thanks in advance. Keith

[MurcoRS]

They should be identical unless GM started using metric threads on them after '75. My 1980 had half metric and half SAE! Drove me CRAZY when working on it. I cannot remember my '76 or '70 having anything but SAE and the brakes were almost all identical. In 1976 they changed the spindle design, that's the only change made to the brakes or suspension until 1979 when 4WD became available.
Good Luck!