After discussing with my buddy Eldon, I have decided not to use the voltage divider approach to power the filaments. They are all wired in parallel and the risk from one of them opening up and thereby taking out the entire set of tubes is too great, not to mention the royal pain in the tush finding a 1.15 ohm 15 watt resistor will be. I decided to order a 2.5 volt 6 amp transformer from Mouser for $13 today and will use it to power the tubes. The other option would have been to rewire them all in series and use a voltage divider to come up with 7.5 volts from a 12 volt source. At least if a filament opens up we power everything down, plus the voltage divider would be easier to construct without having to locate 15 watt resistors.
I love a few select old pieces of equipment, but powering them can be a pain in the empennage. I have a couple sources for the B+ 135 volt supply, so we should be good to go once the transformer arrives.
Meanwhile, I am on the lookout for an old National "doghouse" power supply for the SW-3.