O.K., here is the latest: I picked up the dash support, and the welder was able to attach a new base to the driver's side. He was not proud of the look, and it wouldn't win a prize, but seems solid. He agrees the casting is poor quality, with perhaps some magnesium, or sand, or air bubbles. At any rate, it is much better, and the weld will not be visible when installed. I do believe it is wise to reinstall it, as it supports the dash center, and reduces side-to-side flexing. (cowl shake). I am undecided on whether I will recover the support, or do a wrinkle finish, but there is no hurry, since I still have to take the tub off and etc...etc.
Dennis