Problem Solved.
I sat down and did a full, methodical re-build this morning, and finally established what was wrong.
It turns out one end of the coil was very slightly too high and fouling the bell housing on its very final turn.
I've now reshaped and dropped the coil a little and its reads a normal 1.07ohm and best of 9 - 15w.
I tested the output between each stage and re-built the whole thing with the same parts, for continuity.
Patience and pragmatism wins the day!
Thanks for all your help and concerns folks, this is a great community.
Peace and prosperity to you all.
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