Smudge, re BMW/ Ural / Dnepr convertions.
You would need to find a Dnepr MT11 outfit with a blown engine - lots around as Dnepr made the cranks from chocolate!! The dnepr was designed for hauling a chair unlike the Ural and has a slightly longer frame and the reverse gearbox which is a must as the look on peoples faces when you reverse out of a parking space is priceless!! (also annoys Goldwingers and probably GC

) You also get the TLS front brake which is pretty good.
You'll need a donor BMW engine - go for the 800cc as the 650 is gutless and the 1000cc Will tear the cush drive apart and wreck the gearbox. But be warned the BM engines often need some remedial work on the cylinder heads.
The BM engine will bolt straight into the Dnepr chassis but you have to make up a plate to join the engine to the dnepr box as the engine has 5 mounting studs and the gearbox has4. You also need a series 2 BMW clutch plate which has the same spline pattern as the Dnepr gearbox shaft. You cannot use the BMW box unless you also use the driveshaft and bevel box as the drive shaft spins the opposite way to the Dnepr and you end up with 4 reverse gears!! You also need to make sure the clutch is properly centred or it will rip the clutch apart.
You can run a car battery from the BM alternator in the boot of the chair.
It's a bit of hassle, butthey actually make a very nice handling outfit- or so I'm told by those that run them (my Ural was a solo).
If you did want to try this let me know as I know a couple of people who can probably give you much more info.
PS The M72 is a 750cc sidevalve and cruises at 45-50 mph but willpull a tank up a mountain!!! nice bikes but a bit slow.
......I'll go and put my anorak away now.....