Rance:
Per the 1966 Silver Book (Engineered Vocational Equipment For Chevrolet Trucks), rim width on the 1966 C10 & K10 was 5.50" and optional rim widths were 5.00" and 5.25" with a 6-stud configuration.
Standard rim width on the 1966 C20 & K20 was 5.25" and optional rim widths were 5.00", 5.50" and 6.00" with an 8-stud configuration.
Standard rim width on the 1966 C30 was 5.25" and optional rim widths were 5.00" and 6.00" with an 8-stud configuration.
I hope this information gives you some clarity on your wheel dilemma and good luck with your project.
