I Was Going To Use Cast Rings. If Moly Rings Dont Seal Right Away They Never Will. The Factory Still Use Cast Rings. If There Was A Big Advantage By Using Moly Except Cost Wouldnt Factory Vehicles Use Them
Virtually every new car since the early 80's has come with moly faced rings from the factory. That is why new cars can go 200K miles or more with little or no bore wear. Plain iron rings wear the bores much faster.
Don't confuse the ring material with the coating. All rings with the exception of some very high end specialty rings are made from cast iron or ductile cast iron with ductile cast iron being the premium material.
The rings then come with either no coating on the wear face, molybdenum (moly) or hard chrome plating (chrome has fallen from favor). The premium moly rings use a plasma spray process for appling the coating which is more chip resistant.
If you use plain iron rings the final bore finish needs to be rougher than with moly rings. Just tell the machine shop what you intend to use and they will give you the proper finish and sealing won't be an issue.