I would just get the Walboro and do the 12v mod. Super easy and lots of documentation on Supramania. You will have to drop the tank, though. I also have a brand new fuel filter that you can have. They are pricey, but its been sitting around for awhile and not doing me any good.
Do you know when the head was re torqued or serviced? It is only a matter of time if it hasn’t been addressed. Toyota didn’t torque the head studs correctly from the factory.