Stock pipes should be studs.
No gasket required for ball flanges
Good idea to soak the bolts as they might break. I would not be surprised if you snapped a few stock studs getting it off. Your best bet is to replace them with a pair of BBK shorties so you start with all brand new stuff. Good luck on getting them nuts to come off easily and like I said, don't be surprised when they snap. Mine had so much rust on them they didnt even resemble studs anymore.
No gasket required for ball flanges
Good idea to soak the bolts as they might break. I would not be surprised if you snapped a few stock studs getting it off. Your best bet is to replace them with a pair of BBK shorties so you start with all brand new stuff. Good luck on getting them nuts to come off easily and like I said, don't be surprised when they snap. Mine had so much rust on them they didnt even resemble studs anymore.
If they don't snap, there's also the chance the stud can come unscrewed from the header flanges, depending on whether or not they're tack-welded into place. When swapping out the stock H-pipe from Frankenstang's 80/90 Capristang, one of the studs had a nut so rust-welded on there that the whole stud turned out with it - getting that nut apart from the stud so I could thread the thing back in there was NOT fun.
Make sure to use some SOLID deep sockets - a 5/8" size 1/2"-drive impact socket on the end of a 8" extension has always worked great for me (unless, in your situation, they've got a different-sized nut with those FRPP headers, maybe Metric-sized like 17mm). Using those cheap thin-walled 3/8" chrome sockets will usually just get you into a pickle with rounded-off flange nuts, because the socket wall will stretch/flex just enough to allow it to slip if they're really on there tight.
Make sure to use some SOLID deep sockets - a 5/8" size 1/2"-drive impact socket on the end of a 8" extension has always worked great for me (unless, in your situation, they've got a different-sized nut with those FRPP headers, maybe Metric-sized like 17mm). Using those cheap thin-walled 3/8" chrome sockets will usually just get you into a pickle with rounded-off flange nuts, because the socket wall will stretch/flex just enough to allow it to slip if they're really on there tight.