Yep, Mark that is a #307125 reverse gear. Just got one the other day in a #377876 box myself. I contacted the guy & he sent me the correct part. Told me to keep the reverse gear for my troubles. Like Fisherman6 said the front gear is machined for the front bearing/bushing. On some models (RDs) you can press the bushing in the forward gear out & just put it in a reverse gear, but not this one! Alas, you have to have the correct part.
The gear set break down parts comes once again from a copy of the Common Parts Reference Guide. Couldn’t live without mine. I have several copies from many years. I think I gave Ben a copy. Try to find you one at a meet or eBay.

Dan in TN