I have a Shelter 901 and looking at Shelter dealer's on-line information shows the 501 II as a MC with an output voltage of 0.4mV, which is about the same as the Shelter 901. I use a gain setting of 56 db for the 901 and a load setting of 125 ohms. I would use a low capacitance setting, but I am not sure it matters that much in a MC cartridge.
It looks like the only MM cartridge made by Shelter is the 201
It looks like the only MM cartridge made by Shelter is the 201