UK based?
Rather than try and get your insurance over the net, it might be worth picking up the phone and talking to a real person. The drop-down lists on these sites don't list every bike ever made. The 748cc as you probably know relates to the dohc's.
I've currently got my F2 insured with Carole Nash, however over the years I've also been with Peter Best and Footman James. As for not having a garage - does it have to be garaged at your home? Do you have a mate with a garage?
Welcome to the forum.