Can someone tell me what the stock backspacing would be on a 1972 Monte Carlo or Chevelle? I believe they are the same.

I know they are 15" wheels and 5x4 3/4" bolt pattern. Are the factory wheels 7" wide, or the narrower 5.5"? My wheels look like the "Original Rally Wheels" that Original Parts group sells for Chevelles and montes. http://www.opgi.com/VCProdFrame3.asp?group=11397
However, the backspacing on those varies depending on if you buy the 8" or the 7".

I'm shopping for new wheels online and backspacing varies so wildly on aftermarket rims I need to know what I'm dealing with. I can't find this information (as common as it should be) in any of my books and it's driving me crazy!

Any help would be appreciated.