Thanks for that Roger.
Of the four of mine requiring new masts two had helpful holes drilled through to the underside and with a pin punch I was able to push the stubs out. I do not think they were glued in place None of my duplicates had corresponding holes. So possibly they were the subject of previous repairs.
One of the other had the stubs removed and I just super-glued steel masts in place.
The difficult one was the Enrico C. It had a stub protruding on the underside but it was covered in mazac, not solder and has so far proved impossible to remove. My boxed duplicate was Identical. I was able to force the stub down by a couple of millimetres and glue in a replacement mast in place, but not ideal.