rocky mtn, real source, and the vendors that have ads in VWT & HVWs sell replacement frame head panels, about $100 or so.
I have seen sections in books on replacing the SB frame head and it definitely looks like a challenge. You may want to take a good, hard look at your skills/experience, work environment/garage, tool inventory and the amount of time you will have to devote to this project before you start cutting. Also ask yourself if the car is really worth the time/expense, too. Is the car otherwise sound?
I don't know what a professional would charge for a frame head replacement, but it most likely be substantial.
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" ..... I ain't no bandleader!!"