My H20 came with a bent screw through the bail so I replaced it. The stock Hobie screw is a stainless #10-32 x 2-1/2 inches. I found one at Lowes. If you can find one that's 2-1/4 inches, I'd try that. The 2-1/2 inch length leaves about a 1/4 inch hanging out there. I think you could cut yourself on it pretty easily. I cut the excess off with a hack saw and filed down the rough edge.
I also replaced the worn shock cord inside the boom. It wasn't that tough, just a matter of drilling out the rivets on the end caps. There is a diagram on the Mariner Sails site, here's the link: http://www.mariner-sails.com/assembly.asp?id=23225
. The shock cord will be shorter than the distance you need to cover. To pull the line and shock cord all the way through the boom and around the pulleys, I tied some string to the ends and then fished it through with battens. Then I could pull the string to get the shock cord to reach to the ends of the boom as needed. The parts diagram shows that you'll need 13 1/2 feet of 3/16 line and 5 feet of 1/4 inch shock cord.