[Arran]

I would just disconnect the vibrator power supply from the rest of the radio, leaving the parts in place, and build an off board one connected to the main chassis with a four conductor cable, if there is room inside the cabinet. There are two reasons for this: It leaves the option to a future owner to return the radio to the way it left the factory. It also allows more flexibility with what parts you can use to build the power supply, and what you can build it on, and eliminates the problem of introducing an AC hum from added transformers, or wiring, under the chassis. I think this radio, like my Stewart Warner vibrator radio, had the tubes connected in a series-parallel arrangement to accommodate the 6.3 volt supply, for this same reason they used independent bias cells under the chassis as my S.W did. I also would not be surprised if this set was built by Stewart Warner for Sears, though they were not the only contractor Sears used outside Colonial.
Regards
Arran