Does anyone know what sort of gearbox is run behind a 390 out of a Ford Galaxy?

Two speed?

IIRC toploader (either 3 or 4 speed), C6, FMX

Depends what year Galaxie?
If it's auto and late(ie '68up) it would be a C6 which has it's bell housing cast as part of the case.
If it's pre '68 it's likely an MX transmission which is a precursor to the FMX.
And manuals...once again depends on when? Could be T10(early) or Toploader(late).

Pete.