I finally settled on two loads a 250 grain conical lead bullet (.453) over 6 grains of 700X and a 200 grain conical lead bullet (.452) over 5 grains of 700X. Both loads should keep me in the 800 fps range. Now if the weather ever breaks here we will see what they do.
As far as conversion cylinders go, the gun itself (Ruger Old Army) does not enter into the realm of your concern. Any manual published load will be safe for the gun - the cylinder, well, that's a different story. Ask the manufacturer.
The revolver is stronger than two Sherman tanks. It is the cylinder that matters.