So the mortar assistant is a more difficult conversion.
I used a razor saw to cut through the wrists, and then a Swann and Morton 10A scalpel to remove the head.
After cleaning up the cuts, a pilot hole was drilled with a 1.0mm bit.
This was then opened up with first a 1.5mm, then a 3.0mm bit. The right wrist was trimmed back to allow the helmeted head to fit.
The head was glued in place with liquid poly.
The left wrist will allow the hand to be sculpted beneath the helmet. The right hand will be bracing the helmet.