I have a 6-lug rearend out of a 60-66 Chevy that I got from a guy who had 3.07 gears installed into it before swapping it out for a 5 lugger.
Sorry, that's all I know about it, but it seems like it is possible. I'm planning to put it into my '50 with a 4 speed 3-groove Saginaw.
It will spin the engine at 2500 rpm at 70 mph with 29" tires, and 84 at 3000 rpm. This is about all a 235/261 can handle without it being a real dog.
You may have trouble finding a six lug rearend with gears any lower than that, but if you put in a T-5 with it you would cruise pretty well.
