Lots of people have swapped 2 speed diffs from 420/430s into the open frame 300 series like 318s, 322, 332. AFAIK there is no such swap for the earlier closed frame 300 like the 300, 314, 317. The contemporary 400 series of that vintage has a totally different rear. So I guess you need to specify which model you have and we can point you in the right direction :fing32: