who makes a chain driven diff? just been on z cars site but no price or spec on the one they use?
could try these people - no info on their site though
www.trikeshop.co.uk
An option that I have mentioned on here before is one used by a lot of autograssers.
Get a normal Ford English limited slip diff, and weld 4 discs of steel over the 4 holes in it. Take off the crownwheel and bolt your sprocket onto the
crownwheel location. drill a couple of the discs and fit grease nipples so you can lube the diff, and mount the lot on a pair of plummer block
bearings where the normal mount bearings go.
Not sure about oil/grease sealing arrangements with this setup, never looked closely enough!