safety regs, nira/nhra

i got a few ?'s. first off, i dont plan on being a competitive drag racer. I usually just go to test and tune nights. My race interests are elsewhere, if u know what i mean. However, my car has undergone a lot of changes since i was last at the track. My local track was a nhra, but switched to nira (new owners). Im trying to figure out a) at what times do soft top convertibles need a roll bar (both organizations) and b) is the factory roll bar from vw considered ok (if so, for what type of speeds are we talking?)? This is a daily driver w/ some punch to it, not a specific built drag car. So im not all about making a unstreetable car. As it is, i have no creature comforts (radio/sound deadening, etc) other than i can drop the top when hot. I dont want to install a cage and gut the back seat just so i can make a few passes at the track. Trying to keep my car looking as stock as possible If i remember correctly, i think it was sub 14's needed a rollbar (and how do they define rollbar, i.e.- stock, aftermarket, etc?). But this is from what i heard, have not read any rule books.
Thanks
Sails