The bolt has this washer with tabs that bend down over the nut. You bend up the tabs with a screwdriver, then use a 1/2 inch wrench to tighten or loosen the tension on the spring.

dval, a fellow poster on chevytalk.com - 60-66 trucks and vans, made this suggestion: If I were to add anything... it would be to shoot some WD40, white grease, or etc., after adjustment. <- of course he made this suggestion, after I had it back together. hah!