Just a quick update. I have removed a bit of extra wood from the neck pocket (looked as if the last router pass wasn't quite as big - there was a 1mm high and 1mm wide bit at the base that I took out with a chisel), sanded it square (was just a hair - maybe 1/4mm out) rounded off the one corner of the neck that was a smaller radius and the neck fits very well in it's pocket - I can't see any gaps. Next I have clamped it in place, clamped 2 tuners on and temporarily attached the bridge and 2 strings. Results are in the photo. Everything looks nice and centred to me.

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