Unbelievable the prices now a days, I bought a '28 model A coupe (running on 3 cylinder back in'65) my old man flipped-in his day they were $25.00! The more things change, the more they stay the same-or some Yogism like that.
I never personally saw a 3 speed muncie, or know what the 319 means, but there were 3-speed muncies standard behind 396s in chevelles (everybody bought the optional muncie 4 speed though) so the 3-speed is probably pretty rare (and strong).
Is the muncie quiet? If so, for the money involved I think I would run it until..., and then replace it with a modern T5, I think somebody would buy it even broken at a big swap meet. Another thought, heck, the automatics are far cheaper these days and also have o/d, maybe one of those.