Picked up for free, off a mate, a set off a Rover SD1 front winders, some differences, but so many things the same I think I could mod these to work in a HB?
The four bolt holes don't all line up, but two defiantly do and give the same length on the main bar.
There are two extra arms on the SD1 winders (that can be removed easy)
The only stumbling block I can see is where and or what do the motors interfere with and lastly there is no manual override option.
More when I have had a play around with a tape measure. In the meantime it would be nice to see a picture of the Rover P6 winder and see if its the same as the SD1?