These old flat heads would run on piss. I once dropped a small screw down the throat of my 1948 Chrysler while it was running and it just passed it out the exhaust.
Gasoline was 77 -78 octane in 1948. While it is 87 now, the thing to do is find your sweet spot (timing wise) about 6 degrees advanced to accomodate the newer fuel.
The Valves - if adjusted properly, by yourself - so you know they are done right shouldn't have any trouble.
The Marvel Mystery Oil is good if you like it, but if you run out of gas and have been drinking White lightning pissing in your gas tank would probably get you home also.
With out burning a valve or valve seat along the way L.O.L.
"If drinking don't kill me, her memory will, with the blood from my body you could start your own still" - George Jones