It is So cool. And I'm welcome back anytime.!
The best way of inserting the frets into the slots is with a press. I have a bit that fits into my drill press and holds these little brass cauls that have radiuses. Radii? Pete has a machine that does just that.
Oh, here's Pete:
My neck is pretty chunky though, so I struggled with that.
I finished them the old fashioned way. Hammer time.
Then trim the ends. Which is why we did every other. So you can get the clippers in there.

Voila