OK Stuart,
let me revise that,
I don't know of any older multiple speed auxiliary transmissions that are synchronized.
Some newer synchronized ones that are just a direct and overdrive (some available as direct and under drive)
http://www.gearvendors.com/http://www.usgear.com/http://www.advanceadapters.com/acrobat/saturn.pdf (may not be synchronized?)
http://www.high-impact.net/transmission_and_gear/rangeroverdrive.htmI look at the above units as simply an overdrive, and most of them are just that, essentially just the OD unit from an automatic transmission made modular to be used behind different transmissions.
As far as the "true" auxiliary transmissions available, most older, (and some new ones that are way to big or expensive to consider), I still know of none that are synchronized.
Grigg
