What are dimensions of the B-17 propellers?
According to the maintenance manuals from here about halfway down the page (part 1 page 3) the B-17 was equipped with: 


  
  PROPELLER.
  
  
  Type: Three-bladed, hydromatic, WEE50-473 or 505,
  full feathering.
  Mfgr.: Hamilton Standard.
  Hub: 23E50-473.
  Blade: 6477A-6.
  Diam.: 11 ft. 7 in.
  
  


Part two of the manual has all the installation and setup instructions instructions if you are looking for those as well. 

Hamilton Standard seems to have been acquired by (or turned into) UTC Aerospace which appears to still make propellers. You may want to reach out to them as they may have more info on hand. There are quite a few B-17's lurking around and there may even be one near you that you can go take a look at and possibly even measure.