Some questions on OD?

[cam.man67]

Hearing about how straightforward it is to swap in a 3-speed w/ OD into our trucks, I'm considering doing it I do have a couple questions, though:

1. What vehicles did these trannys come in other than trucks, specifically those with synchros on all gears?
2. What is the overdrive ratio, and how much does that drop rpms at, say, 55 given 3.73 gears?
3. With the added OD, what kind of gas mileage can I expect with 3.73 gears and a mostly stock '80s 350? I get about 12mpg right now.
4. What can I expect to pay for one of these in good working order, and should I pay to have it rebuilt?
5. Anybody got a build thread or a how-to to hook up the linkage into the truck?

Thanks in advance!