Thats a GE VR-II cart on there. One of the better early mono carts made actually. Its moving magnet too, so you should be set if you want to change it to something else. The VR2 is fine for mono, but it'll shred stereo records. It would probably be excellent as a 78 cartridge though. Its standard 1/2" mount, but its rather heavy and that changer (RC-210??) will probably want at least 5 grams tracking weight. If you fit say a Stanton 400 or 500 to it and wire it for mono operation, it should be good to go. Possibly you'll need a headshell weight but thats easy enough to get. The only reason I'd keep that changer is originality. You can do significantly better, even with a slightly later Garrard. An AT6 would be a nice upgrade.