Bruce-when I had my S-10, I had a wonderful soft tonneau made by a company in Michigan called Extang. It had "no drill" aluminum frame rails which attached (with clamps) to the rails of my box. The cover then stretched over the frame. Try your local truck and van supply place and see if they have a "rail tonneau cover" for '73-'87 GM stepside. Pretty sure the newer truck stepside box was almost identical to the '54-up box. Hope this helps.
Regards,
Wannabe
