Are we missing a few steps ?
In your original post, you mentioned "locked in third gear". Most folks having the engine open like that would send the gears to Robinson's for full check-up, once determined good undercut, and purchase a billet fourth gear. Also benefiting from the experience of masters past and present, paying extra close attention to the circlips and their directionality - pretty sure I've read about having the channels enlarged ever so slightly and installing slightly larger circlips.