I pulled out two gearboxes, dated 312 7 and 353 7 so both off a 68 but a few months before your box. Both has the same cover bolts, with three spokes radiating out from near the center and the letters R S C in between the spokes. They were dark phosphate finish and had a separate lock washer. Picture is of the 312 but both had identical bolts. The covers did not have the Saginaw S as seen in the 69 cover above, and look the same as the picture in reply #4 above. Both caps also had the 5689023 number, which I assume is a part #.