>the synchros must be installed ata tranny shop as they are
>part of the shaft and machined into it so i doubt you will be
>doing it yourself..

You've never been inside a T350, have you? The syncro rings, blocker ring, 5th speed gear, and reverse blocker are VERY easily removed from the input shaft. Turn it upside down, and the whole reverse blocker falls off. Remove the exposed snap ring, and pop fifth off with a press (or screwdriver, doesn't really take much). The blocker rings come off with the syncro, as the syncro is the only thing that holds them in place.

If it's poping out of gear, expect the blocker rings and /or dog teeth on the speed gear to be worn down. They're supposed to be diamond shaped so that they mesh and hold the suncro to the gear when torque is applied. If they wear that edge off, applying torque will force the syncro off the gear.

Getting the input shaft out of the case, and then getting the guts reassembled and reinstalled in the case is the hard part. Fixing the syncro is easy.