I've been thru most of the posts in the thread, and maybe this was covered along the way and I just missed it... and maybe it's different enough to need it's own thread. Just didn't want to get barraged with "use a mill" replies, which I don't have.
Looking at inletting some hardware (fore-end rail) into an existing stock. Not really confident in my 'hand-fitting' skills to make a template from scratch that is a perfect fit. I vaguely recall a technique using a hand-held plunge router with guide bushings to follow the outline of the hardware in question and make one (oversize) template... and then use that template, along with some 'back of the napkin' math to figure the correct offset and correct bushing to cut the final recess. Sort of like a router inlay kit, but more generalized.
I probably have a book buried somewhere (moved this spring and the contents of every bookshelve I had are still in boxes in the shop) that covers this, just haven't found it yet. Somewhat surprisingly, I haven't had much luck finding anything searching forums or YT - granted, that was before someone mentioned the term 'inlay kit', so I do have few more leads now.
@joshb does that ring a bell? Any suggestions there?