[peterux]

Hi Jason,
welcome back to the forum although things are a lot quieter here these days as there are fewer of us left. So sorry to hear about your condition and I hope you can still get out about in your Sportster.
Retrofitting an auto box is an intriguing project but quit a major project. My biggest concern (which you may have already checked?) is whether the BMW auto box will fit in the steel tunnel. Mike Garner might know if anyone has fitted an auto to a Cabrio which I think has the same dimensions as the Sportster chassis.
Maybe an alternative idea would be to fit a servo to the clutch hydraulics. From a bit of googling I found this is a not uncommon upgrade on MGB's to make the clutch pedal lighter. People seem to use a standard remote brake servo. Maybe you could fit one high up in the passenger footwell as I doubt there is enough space under your bonnet.

all the best,
Peter