Any B series tranny will work. I am assuming your current tranny is cable, so any cable B series tranny will bolt up. Any B series hydraulic tranny will bolt up to a hydraulic cable system.

Most of the times, a used tranny can be cheaper than a full overhaul. It wouldn't make sense to do all that work for just a synchro. If you can find a cheaper compatible tranny for a decent price, that would be a better choice than a full overhaul.