later TR6 gearbox in early TR3?

[Dan Buettner <danb@thelittlemacshop.com>]

I was just made aware of a late TR6 overdrive gearbox for sale, and 
am wondering if anyone has any experience fitting one into a TR3. 
It's a J-type OD.

Anyone know if this is possible?  I don't want to modify the 3 much, 
if at all, to fit it in, but internal modifications (different 
clutch, etc) would be fine.

Dan