The older SFG-2 models used a steel balance beam with ferrous content and would attract to a magnet. At some point later in the production history this part material was changed to a non-ferrous metal which is not attracted to a magnet. (looks like stainless steel)
I have one that I purchased in the late seventies. It has the non-ferrous balance beam. Therefore, safe with MC or any cartridge with a strong magnet.
I also use an electronic vtf scale. A so-called "Micro-Tech" that was sold by Express Machining. In practice both the Shure and the Micro-Tech produce identical readings. And the Shure was far cheaper. But the Micro-Tech is more convenient and quick to use. No balance beam slider to fiddle with, just place the stylus on the little shelf thing and read the reading.
I still like the Shure, however.
-Steve