Every builder out there works on other builders stuff. If it's a factory cylinder or a Cheetah cylinder they were all designed by someone and a builder must check the current specs and resign to meet your goals.
If you deck the cylinders base or if you throw in a stroker or long rod crankshaft... YES the piston will have a positive deck height. Just like every stroker motor made before the aftermarket cylinders came out.
I'm not sure about sulfer content in avgas or race gas but it I know there have been problems with pump gas having too much sulfer content. The majority of the problems it caused was fuel gauges sticking and people having to replace their fuel level sensors in the fuel tank.
The OTD price depends on what Cub motor you want to build. 65mm bore stock stroke would be around 900 for a cleaned up cylinder. Add new gaskets, longer rear studs, brass plugs for the bottom of the cylinder, and two pistons. Out the door I would say 1100. If you already have a stroker crank the price would still be about the same with the exception of the more expensive pistons. Same goes for the larger bore.