Yeah, I was lucky, the guy who tackled this on my car is an amazing precision welder...One more thing to take care of--really try to insulate the aluminum from the steel frame--electrically. Meaning the best is to put a piece of tape (even, duct tape) between the steel frame and the aluminum...or paint, anything that keeps the electrical connection in being made.
The opposite approach was in the Mangusta as well, using copper rivets to hold the dis-similar metals tightly together...All those rivets in the engine covers between the aluminum panels and the steel braces, they are copper--and also copper is used for the intake ports (the aluminum castings in the rear sidewalls near the battery/starter solenoid)....or of course, on the hood. Last place I can think of is on the hood, where even I had a couple of pinholes where the steel cross brace at the midpoint of the hood just touched the aluminum skin...
Greg, its always a thrill to see your pictures---Lee