Those cams are used and also use 10mm fastener hardware.
If you are intent on using the 03/04 Cobra cams, I have a brand new set, never run, that have been drilled and tapped for 1/2 x 13, 8740 ARP 12-point bolts that I'll sell for the same $300 price. ARP specs the torque on a 10mm 8740 fastener as 62 ft/lbs. The ARP spec on the 1/2 inch 8740 bolt is 125 ft/lbs. Ford specs the torque on their 10mm TTY single-use fasteners at 30 ft/lbs plus 90˚ of additional rptation. The ARP fasteners are reusable the FRPP fasteners are not. The cams will need both the ARP bolts and four ARP washers that are 0.275" thick. Both the 12 point bolts and washers are standard off-the-shelf ARP items available through Summit.
ARP offers the identical thickness and diameter washer for 7/16" and 1/2" bolts. The 7/16" is $9.99 each and the 1/2" is $11.99 each. If you have drilling facilities, you can save a little on the washers by using the 7/16" washer. The 7/16" washer part # is ARP 200-8717
and the 1/2" washer part # is ARP 200-8749
. The Summit pic for the 1/2" washer is wrong. The part # is not. The 12 point bolt part number is ARP 627-1750.
I would recommend the 7/16" washer drilled out for the 1/2" hardware.
Before you drill the washer you will notice one side has a chamfer as delivered from ARP. The chamfer is there to avoid the radius on the underside of the 12 point bolt head. If you just drill the washer without duplicating the clearance chamfer you will eventually snap the head off the bolt. The head normally leaves the bolt at a relatively high engine speed bending lots of valves, breaking guides and sometimes dropping valves that punch holes in heads and cylinder walls — and I haven't even gotten to what it does to the pistons. Be sure to re-chanfer the washers.
Let me know what you would like to do.