The 301 uses the same bobbin and case as the featherweight. It's a vertical bobbin machine so should be good for FMQ as well. Other 300 # machines aren't in the same "family" as the 301. The 400 and 500 slant needle machines use a drop in class 66 bobbin. I have a 401A and am very impressed by the quality of the machine. IIRC there are other 400 # machines that aren't slant needle machines. The 404 is a straight stitch only version of the 400 series slant needle machines.
Rodney