Fan shroud size vs fan blade
 

So I am very pleased with the cooling now I get with the new Dewitt's Aluminum 2 core with 1-1/4" tubes. However, I need to address one last issue. My fan shroud and fan blade sizing isn't correct. The shroud measures 21" wide (best I can tell - not easy measuring with fan in place). And the blades appear to be 18". Too much gap between shroud and fan and not efficient pulling. What I assume is the shroud is a big block shroud and the blade possibly for small block. What is the largest stock 772 (7 blade) GM made? 19" 19.5"?

As far as I know the 772 only came in one size. A different size would require a different part#. Honestly don't remember the size of the 772, 19" sounds right but can't guarantee that.

772 fans are 19" or 19.5" depending who you ask. The fan shrouds are different for 70 vs 71 to 72. Also does your fan have the curve tips? The fan shroud on my 70 does not cover the entire radiator, leaves some of the drivers side uncovered.

Fan should be 1" less than the shroud diameter. So if you took a compass and drew a 4" circle and drew a 2" circle inside of it, that would equal 1" clearance at the tip of any blade. So if your blade is 19" and your shroud is 21" your in like flint. Just remember the fan should extend into the shroud at least 1".

Another thing you can do is put a panel on your radiator support to block the open space and force the air through the radiator. www.undercoverinnovations.com is where I got mine.

Correct. That is why I was asking about a 19" fan-which would pair up nicely with a 21" shroud. I am being told there is not stock 7 blade 19" fan?