That date is prior to 1969 with some exceptions for the 1969 model year.
Originally Posted by polarlyse
I think you'll find that with the exception of some really vintage Airstreams you will find them all to use the 2 5/16" ball.
Bill Kerfoot, WBCCI/VAC/CAC/El Camino Real Unit #5223
Just my personal opinion
1973 Dodge W200 PowerWagon, 1977 Lincoln Continental, 2014 Dodge Durango
1979 23' Safari, and 1954 29' Double Door Liner Orange, CA