B40/C15 steering head cup removal

[Stubaker58]

Having sourced a frame loop that has a proper number (and thus some chance of getting registered) I now need to strip it for blasting and minor welding.
I'm used to Bantams where the steering bearing cups come straight out with a blow from a straight drift.
I've made up a bent drift (from an old junior hacksaw), filing the end flat ... BUT there is virtually no lip to get behind.
How have others managed to get the races out?
Thanks