I'd suggest swapping the entire synchronizer assembly, including the sliding collar that the shift linkage engages. That rust will polish off with a little bit of work with a wire wheel on a bench grinder. Mixing and matching synchronizer parts, except for the brass blocker rings, is seldom successful. I always put a small scratch mark on the mating pieces of the slider assembly with a diamond-tipped scribe so the wear pattern of the male and female splines isn't disturbed.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!