Here is the latest and last reply from Ventura -
""Hello Mark
Thanks for your reply and my apologies for not being specific in replying to your questions.
The PF16/B rack as specified for your model is not reversible and can only be used facing to the rear, however, the pack can be used in either direction, facing forwards and resting on the pillion seat or to the rear over the carrier. We recommend that when riding solo with one pack that it should be carried facing forward over the pillion seat.
By your photos you have the correct system for your bike and the 748BIP is supposed to be mounted in the same position as the 996BIP on our website.""
So that's the end of that. For the 996BIP and 748BIP the pack can be over the seat or the back of the bike, but the rack can only be out over the back of the bike.
Thanks for your help guys.
Mark