Easy fix, GMC can do it for you, hes near you? If you wanna save some dollars, get some 3mm alloy plate, make a cardboard template and then cut the alloy out to the shape of the fin. Then Vee the join out for the weld. i also set up the new fin with blocks, bits if metal or what ever to get it in place so then all i need to do is drop it off at the welder and all he has to do is look at it and then run a weld bead and its done and he doesnt have to much around anymore with it costing me $. Make the fin oversize first, then after its welded on and you got the barrel back you can then shape the fin to suit. If done well, you can not tell a fins been welded on.