Two of the classes I run have been combined at roebling (LWSS and ULSB). Can you register for both? How would they determine positioning - I assume they would compare your finishing to the other riders in each group.
Yes you may enter both classes. You will be given two grid positions. Electronic scoring tracks the running order and in a combined event like that, we manually separate by class for scoring.
Make sure you let the pit steward know that you are entered in both classes so that you do not get "meatballed" for the "wrong" grid position and that scoring is reminded of your double entry.
Good luck!
If I might add you must run a bike that is legal in both classes ( your ULSB, Ultra lightweight Superbike, I assume and it must be LWSS legal, IE DOTs, stock wheels, legal engine mods, etc ) and must take the inferior grid position(IE the one in the second wave or furthest back grid postion)