What's an acceptable replacement for this? I don't see any Homeywell
4064E's anywhere. Mostly 4064B's or some other letter not E.

It's just a fan limit switch for an old gas furnace with an 11.5" shaft
that goes into the furnace. I suspect that the replacement model
number is different because I doubt anyone would really want an exact
replacement because of the crappy push in electrical terminals on the
one that I have. My guess is that any generic one that has the 11
shaft and is adjustable would work, but would like to confirm here.