View attachment 5032 A later update to this thread for those fitting TTi boxes...
I have a Mk2A 850 fitted with a Mk3 850 engine cradle and swing arm. The TTi box "almost" fits straight out of the crate, with only minor modification needed to the cradle on the drive side - approx 6mm/ 0.25" of material needs to be removed on the drive side plate in an arc from the 9 o'clock to the 10 o'clock position, as viewed from the drive side.
I'll post some pics shortly.
If TTi made one more simple cut to the gearbox housing on the same plane as the drive side mounting surface, the TTi box would fit the Mk3 850 cradle with no modifications required. I'll send a video I made of the area needing attention to Bruce Verdon, the owner of TT Industries. They're less than 5 mins from my home. Bruce told me when I met up with a few weeks ago that he's been (pleasantly ) surprised by how many road bike orders he's getting for his Norton box these days. Until recently, most of the orders were for race bike use. With a few minor cuts to the housing in the manufacturing phase, they'd be a much simpler fit for road bike use.
Aren't the mounting lugs on a featherbed gearbox case .25" wider than a Commando? It sounds like they only want to make one case for all AMC gearbox applications.