So after lots of searching and ascertaining that it is not possible to fit HD detachable saddlebags onto softtail Fatboy S that has passenger floorboards- success. The credit is not mine but the skill of the Southampton (UK) HD dealership. Took about 3 hours with the rear indicators relocation. The bags fit a treat. To be honest they also look the dogs bo****ks, so well happy.
A great result for SHD. So yes it can be done