[Arran]

You could try finding a large electrodynamic of another brand, I have a 15 inch Magnavox that came out of a Northern Electric/American Bosch console. I don't know if Magnavox, Utah, Quam, Rolla, or any of the others made 18 inch pedestal speakers though.
Out of the old American speaker manufacturers Jensen is the only one that seems to have that sort of cult following among audiophools, probably because it's one of the last ones standing, sort of like brand Z was to TV sets and other consumer electronics. Not to bash Scott or McMurdo-Silver but quite frankly any audiophool that thinks an electrodynamic would deliver higher fidelity sound then a PM dynamic must have cotton shoved up their ears.
You could go with a PM replacement, but I would suggest using proper filter chokes in place of wire wound resistors, not only do they not produce heat but they are far more efficient at filtering AC ripple without causing a voltage drop under load.
Regards
Arran