If you're used to looking at ABDG and H series the timing marks are not on the flywheel face. They're on the rim to be viewed through the hole under the pear shaped "flap with one screw in it" up on the forward top of the flywheel cover.
What you describe flywheel wise sure sounds like a taper lock as Loosehandle said. It too should have marks on it. My taperlock does though my tractor is a Diesel.
Like Wilamayb said though... I'd NOT tune by ear unless it's a modified engine! There yer on yer own! They prescribed a 10° after TDC (static timing) for a reason on the gas & LP models. That reason is at least partially starter parts!
After that start it up & you SHOULD see it running 15° advanced at 1000 & up! Much more than that & they'll knock right soundly under load.
Make sure the advance works right in the distributor! If it's -10° static and reaches +15° at a thousand, the mechanical advance is working as it should.
Hope that's helpful.