Well, the 1966-68 trailers are all the same. On the Vintage Airstream Club's website, there is a 1968 Catalog which states the "outside floor width" is 7'-4" (on page 28 of .pdf/pg 26 of brochure). Now I know that the sales brochures tended to "round off" trailer lengths, but I'm not sure about widths.
Vintage Airstream Club - Past President 2007/2008
WBCCI #1824 - DenCO Unit Past President (2005)
AIR #30 - Join Date: 2-25-2002