Rover gearbox problems

[relative4]

Yesterday I made the first test drive of my conversion with an SD1 engine and gearbox.  The engine is running great, but the transmission has issues.  First, it make a deafening whine under compression braking, in any gear.  No crazy downshifts, just taking my foot off the gas.  Second, once I get into third or higher gear, it starts a nasty clicking.  The speed of the clicking is proportional to the speed of the car, continues unchanged when I take it out of gear, and doesn't stop until I stop the car.

Thoughts?

Thanks,
Billy

[Dawie]

I've no direct experience with these 'boxes, but the former noise suggests rearend and the latter suggests speedometer drive. What is the provenance of the rearend? Is the speedometer connected and how does the needle behave?   -D