I just thought I would pass on that I bought a pair of these 1.5" wheel cylinders off eBay for $90 shipped. The Dorman part number was W3677. They are listed as fitting 47-50 GMC models, but according to my Mk I eyeballs, they are the same as the Chevy ones. I will post back with a follow up after I get them.
http://www.ebay.com/itm/331809635528?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT