Brass cases will be too thin unless you get the machined ones. Rem plastic cases worked for me in my 20 ga paradox. They grip the bullet well so you don't have to worry about crimping. For load data, look at loads for the same weight of shot. The conical bullet I use weighs right around 500gr (it's the WR design for their fauneta). You will have to put some felt wads in the case to take up the space. I also used plastic obturator wads just to be sure of getting a good seal. Thus loaded, this gun is WAY more gun than a 20ga foster slug. Waaaay more.
Fine English, American and German Double Shotguns and Rifles