Attached are 3 photos and my drawing of a 1969 Camaro Coupe J-Bolt & Wingnut, GM # 3949607 & GM # 9785616. The wing nut has 8 "dimples" on the bottom side. This was with a 1969 Camaro bumper jack, 32 1/4"long, stamped "UN" on the jacking mechanism, and dated "9A" (1969, Jan.) on the rivet head that I bought at a salvage yard in Pepperell, MA back in the 1990's. I have many other J-bolts that I am doing research on.
Dave