Good day Jim,
While I don't have any experience with your particular OMI brass model, I have reached out to NWSL in the past with questions about a regear project I had for another locomotive. They were helpful, and they pointed me to the product number found on their online catalog. I still recommend emailing them via their Gear Request Form from their website:
Gear Request FORM
Also, I checked over on the Repower and Regear Yahoo Group, and found a thread from a person asking about regearing an OMI locomotive. Here's a response I found to the thread that may be helpful for your project:
"...my own HO OMI Milwaukee L3 USRA Heavy Mikado also had a failed gearbox
identical to yours, the slippage occurring between the worm itself and
the idler worm gear. The roof of the cast zamac distal worm gear bearing
housing had broken through. Although this alone would have allowed
enough upward movement of the worm to disengage it, it is possible that a
poor fit to begin with caused enough momentary pressure between gears
for the housing to have been broken through anyway
Be that as it may, do not waste time on the current OEM gear box, but
simply retire and remove it (along with the axle gear), bag it, tag
it, and put it in the green box for the next owner to know what was once
there, and what you had to deal with. Replace it with a new idler NWSL
box, #150-6 according to my records.
I also replaced the neoprene rubber drive line connection with a segment of silastic R/C fuel tubing."https://groups.yahoo.com/neo/groups/repowerandregear/conversations/topics/10331My recommendation is still to reach out directly to NWSL and see what they have for your specific locomotive. I do highly
Hope you find this information helpful. Good luck with your project.
Have a wonderful Easter weekend.
Jon