Take your time to repair it properley as those barrels are tough to find.
Suzuki head studs are a good thing to make a repair.
The Suzuki studs are shouldered and will require either the barrel or the head to be counter bored to accomodate the shoulder.
The Suzuki Stud has a M8 thread on the head nut side (visible when stud installed) and a larger (M10 IIRC) on the barrel end.
Remove the barrel and use a drill press to make sure it is all square (cutting a hole into a thick piece of ply with a hole saw makes a nice solid base to support the barrel).
Drill the barrel to the recommended drill size for aluminium to accept the appropriate tap. Counter bore the Barrel approx 2-3mm to set the stud level with the deck or just below. You need to use a broaching tool to achieve a flat bottomed hole. If you cannot borrow one, I have sacrificed a drill by flattening the point to do the job and it will work if your careful and use a drill press with your job securely clamped into place. (success is reliant on careful set up and secure mounting of the barrel)
Tap the barrel using plenty of cutting lube and clean the threads out thoroughly before installing the new stud.
The studs you need can be found on 1980 RM's and probably lots of other models as well. Check the parts diagrams on line for other models which may be available as donors or just buy a stud from the dealer.
When you re install the head, use plenty of oil on the threads of the head nut and the face of the nut flange to head surface interface. This will help achieve a more consistent accurate torque and therefore even clamping pressure by overcoming the run on friction on when tightening. Make sure you check the nuts all run on smoothly before attempting to tighten them. Same goes with the Barrel base nuts.
Try to avoid using bodgey fasteners to make a quick fix, you will just wind up paying more when it fails and screwing over the next bloke who dismantles the donk.
Good IT250K Barrels are really tough to find! And every Enduro nut deserves to ride one of those bikes in thier life.