Or perhaps a Fuller 6 speed, model number starting with FSO... FSO-6406A, or FSO-8406A. I don't know much about those though, or how easy they are to find, only in reasonably new trucks, medium duty size. OD ratio is 0.78, first gear is 7.05, weight is about 375# installed including oil. Could be more weight than you are looking for, and a custom adapter may be needed unless you can find an SAE flywheel housing for your engine?
Allison 6 speed, same size as from a Duramax, has about 0.64 for the second OD ratio. That is about as good as you will find for an OD ratio. I know of a new never used one for sale, with all the electronics to work on a non computerized engine, price is realistic, but expensive none the less.. Not sure how you would attach it to the 6 cylinder? I believe it has an SAE housing on the transmission.
Grigg
