The recommended timing is somewhat arbitrary of fuel used, and based on the cam grind for the build (my guess where you are getting your recommendations from.)
Gas doesn't need as much timing since it has a higher flash point than alcohol, BUT, compression has more to do with determining proper ignition timing in my opinion. Sure, carb set-up, exhaust, intake flow, etc, all factor in with timing advance, but with the very low compression of our flathead engines, they are not real finicky on fuel (gas or alcohol.) Just make sure that you jet your carb correctly for the fuel that you are running, and don't get carried away with too much timing advance, or you'll run into an overheating problem. For short blasts, you can get away with considerably more timing (detonation & knock.) For longer runs, you will want to avoid hammering on that piston too early (ie too much advance.)
I think you'll be just fine with 30 & 33* with those two cams, respectively, but the rest of your build will have to work with that set-up.
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Thanks and God bless,
Brian Carlson
Carlson Racing Engines
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