OK, thanks. Followed your suggestions, used jewelers driver & managed to finally get it. Was originally holding it all in my hands too but finally put the flat faces of the bolt sleeve in a vice (cushioned) to get max leverage on the selector & plunger, could never really get the plunger far enough in to just push the selector on by hand but got it close enough to tap gently with a rubber mallet & nudge it over the lip.

The project piece is on the right. Appreciate it!

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