360 Plug help

I don’t know if current Speed Demon carbs have screw in air bleeds, but they didn’t in the beginning.
I found early Demon carbs to not have very good street calibrations.
(I used to actually thread the holes and install changeable air bleeds in the more problematic ones)

If you’re determined to keep that carb, I’d suggest installing a wide band O2 A/F gauge in the car.
That way you can get a visual aid in seeing what the carb is doing under various driving conditions.

You didn’t mention what camshaft is in the engine, but if it’s nothing too wild, and you’d rather just swap the carb, I’d probably lean towards an Ede 650AVS.