Grigg,

They were made in Healdsburg, CA years ago by a family owned company. They're a cast aluminum, finned stylish box, very light and functional.

My box is direct and 0.29:1 overdrive and rated for 20,000 GVW (?).

This company still makes overdrive units, but now they focus on the "antique car" market....Model A's. They have relocated to Colusa, CA.

I have enclosed a link to their new product. These gear splitters are few and far between, but I think it's because folks who have them keep them.

As you mentioned in your post above, this isn't really a auxiliary transmission, but merely a OD unit.

http://www.model-a-autoparts.co.nz/overdriver.php

Stuart