I did this years ago. I cut a piece of pressure treated pine lumber and used it to raise the mast 1 1/2″. Aged pressure treated is best because you can epoxy it in place. I cut 1 1/2″ off the bottom of the mast and kept the cutoff piece. The base is fastened in place with lag bolts. Remove the torsion bar and lag screws to remove the base. Take it to a welder to have a replacement made. I don’t remember what I paid but it wasn’t expensive, maybe $200. Bring the cutoff piece to be sure that the replacement is fabricated correctly. Coat the replacement well to keep it from rusting. Get longer replacement stainless lag bolts. Cut and drill the wood shim and put some epoxy on the bottom when you replace it. I didn’t have to cut the torsion bar. There were sufficient threads. I’ll take a photo if I get a chance.