When I acquired my'37 last summer, someone (I can't recall whom, perhaps someone at Vintage Power Wagons) advised me to use a concoction of Seafoam, lead substitute, and Marvel in the tank, and if not frequently driven, also StaBil. So I ordered a case of lead substitute (RedLine product) and SeaFoam, and bought a big bottle of Marvel, and poured the suggested mixture into my tank. I can't now recall what proportions I used. I think the StaBil was why my truck started so well after sitting for 9 months with the same fuel in the gas tank, with the bed off and the black painted gas tank in the sun. I agree that finding a station with non-ethanol gas is pretty important too. Where I live in UpState SC lots of stations now have the ethanol-free gas, I think because of all the companies around me that are in the lawn maintenance business, and need it for their power products.
Now that I am back on the road with a completely rebuilt engine (and other components, like brake/fuel/vent lines and so much more, I only use the ethanol-free gas. I don't need the lead substitute nor the Marvel and Seafoam additives, as my new valves and seats are all modern and new.
Enjoy the ride, and there is a wealth of experience on this and the other forums dedicated to these sturdy beasts.
NAM VET