Steve, this thread went into space saver some. The 1970 and 1971 assembly manuals show how the space saver was stowed. Check Option N in your 1972 manual and see if it shows something similar. Brackets were in a substantially different location, according to those manuals. However, since the brackets were supposed to be welded in place by Fischer before reaching GM, I'm not sure how they knew which bodies needed which brackets. I guess it would be similar to how they handled four speed versus automatic, etc.
http://forums.maxperformanceinc.com/...d.php?t=649232