Help finding a P-Bass neck; vintage dimensions

I've been toying with the idea of trying to build my first bass. I'd like to build something like a Vintage 62 or 57 4 string P-Bass; but I haven't been able to find a replacement neck (warmoth, Allpart or US Custom) that has a 1.75 inch wide nut. The closest I've found is the 1 11/16" wide nut. I know that is only 1/16" short, but I'm surprised that I can't find one. Does anyone know where I could find one (new not the used necks for sale on Ebay)?

Also, I'd like to have 20 mm string spacing (I'd really like 21 mm string spacing); which bridge would work for this (Hipshot or Gotoh?)? And is 20 mm string spacing going to work on a Vintage P-Bass neck?