Had to jump in here with my 2 cents. My bike is a '77 K7 with the bracket. PO screwed up the bike and frame in so many ways, one of which was just throwing any nut and bolt he thought fit into an area. So when I inspected the bracket and realized the bolts were seemingly way too long, I went to look into it - checking to see the correct size and whether there should be a hex nut or flange nut and much to my suprise (and eventual irritation) I could not, for the life of me, find that bracket nor the accompanying nuts and bolts. Ended up figuring out that the 2 bolts that go thru the bracket/frame are 8x65.
More to the point, it's quite an interesting story!