bed cover for '68 stepside

[mdimarzi]

I'm trying to find a soft tonneau cover for my '68 k10 stepside(preferably white). i checked out a company named extang who makes white tonneau covers but they do not make one for a stepside before '88. i was wondering if any knew anywhere else i could find one or if someone knew the bed dimensions so i could find a cover for a comparable size and make it work. i would measure it myself but i am in Indiana right now while my truck is in massachusetts. thanks for the help