The single bolt with washer is because the Edelbrock castings require two long bolts as opposed to one for standard LA castings. When you break out the instructions for your second casting, read that part-it's in there. (should be positions 4 & 5)
They anticipate you'll use ARP bolts to fasten them on (why not? new heads-should use new head bolts), and the ARP kit only comes with 2 long bolts-1 per head.
