Ah! Found some info. It seems that there are / was A,B,C, and D widths. B was standard though and all others were special order only. So virtually all vintage Fender guitars will have a B width neck and most modern ones too unless you're able to get one made to order.
The following info is from the Fender Vintage Guitars Info Page
http://www.provide.net/~cfh/fender.html
Neck Width.
From March 1962 to 1969, Fender marked their necks with an "official" neck width letter at the butt of the neck (in front of the date code). The "B" neck width is the normal width, as used on about 99% of all Fenders from this period. All other sizes were available by special order only. Also all pre-1962 Fender necks have a 1 5/8" nut width (though I'm sure there are some exceptions, but none I have seen).
* A = 1 1/2" wide at the nut.
* B = 1 5/8" wide at the nut (normal size).
* C = 1 3/4" wide at the nut.
* D = 1 7/8" wide at the nut.
