I had a long conversation with Jack Obrien (got the impression that it's not possible to have a short conversation with him), when I called to ask about his heavy duty detent springs.
Jack is a metallurgist by trade. He went into great detail about the difference between his gears and the stock Spicer and the TeraLow gears. There really is no comparison between the manufacture and heat-treating of his gears and any others. This accounts for the difference in price.
Unfortunately Jack does not have a Web site, nor does he advertise. He says he relies on word of mouth only. I did find out that he offers a full range of gear ratios for the Dana20, not just the 4.86 (or whatever that ratio is) gears that have been offered by a couple different vendors. He also offers a full range of rebuild parts (most of which are better than stock) for the Dana 20, including shift forks.
When I talked with him, maybe a year and a half ago, Jack claimed that he could build a Dana20 that would be as strong as an Atlas, for something close to the same price, but, obviously, with none of the fitment issues.
I have TeraLow gears installed also, and am very happy with them. But, if I ever get to the point where I feel the need to upgrade my transfer case, I will give Jack a call.