The problem with original fans is one of "rust" - well besides cracks.
Hold the blade between your fingers and feel if there is any "thickened" portions of the blade - a "bubble" if you will. What has happened is water/moisture gets between the two leaves and rusts - and rust occupies more space than the metal it came from. You're feeling the rust pocket.
THIS is why I would never try to repair a cracked fan - you're repairing something which is fatally flawed in its inception - and with 80 years of service to boot.
The last iteration of "airplane" type fan MIGHT be worth fixing as it is "single thickness" for 70 percent of its blade length, and what is doubled near the pulley is "seal welded" all the way around the perimeter.
Vince Falter calls the last fan iteration a "Model B" fan which is probably closest to fact as very few Model As were fitted with the better fan at the end.
http://www.fordgarage.com/pages/twobladedfans.htm
Joe K