Thanks for the feedback. In pic 1 the clamp is fully on which means the end of the neck is pressed against the body (showing the gap under the heel). In pic 5, I've released the clamp a few turns meaning the neck has settled to rest flat against the body (and removed the gap). In my (first timer) view, it seems that the heel of the neck is slightly thicker at the far end (the tongue) compared to the heel meaning that if I were to glue it as is, I'd be left with a gap (if the tongue was fully glued to the body) or no gap (but the tongue would be raised away from the body within the humbucker cavity). Either way, the bond would be weak/incomplete?

Ahhh, I've just re-read your 3rd paragraph and now I think I understand - will retry that approach tomorrow with 2 clamps. Thanks @fender3x 🙌