I managed to derust the original speedometer, and with a drill driving it, it nearly works like it oughta. Problem being: The weather sealer plastic crumbled completely upon disassembly. It's a formed plastic channel and I'm not entirely sure I can get along without some kind of equivalent.
Oh...yeah, and the thread for the speedo cable is galled all to smithereens.
There's plenty of used $50 Ca95 speedos on fleabay, but the only N.O.S. 0 mile MPH one is currently going for $300...which is more than I spent for the whole bike!
I'm also considering fabricating a block-off plate and using something like this:
Obviously a 140mph speedo on a Benly is a MASSIVE amount of overkill.