Congratulations on getting the Dort running, it must have been a sweet sound when she fired up.
While I don't know the compression ration of your Dort engine, most of that era have very low compression, below 5 to 1. This was because of the low octane levels of gasoline in those days, I've read where it was as low as 67 octane. Lead wasn't introduced as an additive until the late 1920's, so the most fuel back then was really unleaded, So it should be necessary to add anything to your fuel as most low compression engines will run fine. However, I do from time to time, add a little Marvel Mystery Oil to my fuel tank in the Winter.
I use the lead substitute in the gas for my '31 Durant 619. Who knows if I need it, but I heard that you should in engines w/o hardened valve seats. Sounds good, so I do. For the little driving most do with our old cars, may not need it, but I'd raltehr not find out in a few years that I should have.