Bob, I had to make all-new heavy-duty [3" x .120" square steel tubing] frames for one Austin-Healey 100/6 and one Triumph TR-6...The original frames were pressed & welded steel sheet, very thin, and rusted out to the point that the doors wouldn't close right...I was lucky in that Robert Bentley sold a manual with every dimension you could ask for and detailed drawings, so I had no trouble cutting & welding a new frame...
...There's no way I would consider putting a V-6 in an old MGB without a stout new frame...
