[Excaliber]

The synch rings will NOT require 'bedding in' or 'burning in' as you call it. There should be plenty of clearance even with totally new parts for them to be 'free' with slight movement back and forth even.

If the synchro brass RINGS are binding upon final assembly I would have to conclude they are not installed correctly, they are being 'crushed' when the tail shaft is installed. This could be due to the incorrect use of the detents in the synchro hub(s), as noted above. I know of no way to determine which detents fit which hub, if one set is longer than the other then you have your partial answer. The question then becomes, do the longer detents go in the front or the rear hub?

One thing for sure:
The detents (actually called synchronizer keys) ARE different for the two hubs in question. I would guess it DOES make a difference, especially if their 'mixed' in that you have two rears in the front, one front in the rear hub, etc.

Also bear in mind the synchro HUBS are a 'matched set'. What this means is the inner hub splines fit into the outer hub splines in a such a way that the two parts move very smoothly within each other. While the inner hub will 'slip into place' within the outer hub at any position there is only ONE position that 'feels' smoother and fits better than any other position. While this will NOT impact your binding problem it WILL impact how smoothly the trans shifts under load. Once you have lost the correct relationship between the inner and outer hub it almost impossible to determine it's optimum position again. They should be marked before tear down. You can get pretty close by using a magnifying glass and looking for the 'marks' left on the 'spline' of the outter hub by the synchro keys. That gives you a one out of three chance of correct installation. Put the inner hub in and slide it back and forth. Hangs up just a little? Try the next position, keep doing that until it slides as freely as possible.