Thanks, everyone -- that's a lot of great advice!

3mm plug cutters seem hard to come by, but I do have some flame maple veneer from a previous project.

Seems like the best option will be to cut the headstock first; then there will be some offcuts where I can drill some small holes and then try both Simon's suggestion of filler and McCreed's toothpick trick on it, then try a coat or two of the planned finish to see which is least visible. If both wind up being too obvious, then there's always the veneer or the mounting plate options to consider -- in my last veneer project I was able to disguise the line at the edge by using a nail file to bevel it, and it's pretty much invisible unless you look very close -- hat tip to Jeffrey Stephenson (who does amazing wooden computer cases) for that trick.

I had less time than planned this weekend, but was able to take the measurements after a dry fit of the neck and the body. These kits have the holes for the bridge screws pre-drilled:

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Basically, the same as christodav's Purple Monster -- even down to what looks like a ding from tooling above and to the right of the centre bridge screw hole.

Nut to the crown of the 12th fret is bang on 324mm, like you'd expect.

However, in order to get 12th to the bride saddles OK, they need to be all of the way forward:

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...that is the tips of the adjustment screws are basically flush with the saddles. Set like that, the middle and top saddles are within half a mil or so, measuring to the top of the saddle where the string will "leave" it:

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The bass saddle has a shorter adjustment screw, though, so it's about 5mm off:

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From what Simon has said elsewhere on the forum, it sounds like that *may* be OK. All intonation adjustments, if I understand correctly, are pretty much certainly going to be moving the bridge saddles away from the nut. My only concern is whether having a starting point of 5mm back is going to be too far for the two bass strings.