Gee, I wondered if you might post a question or two here...... I saw your boat last weekend after you had lauched her, nice boat!
I own the bright yellow Day Sailer II moored off Willow St and would be willing to offer any advice or help I can. I had noticed that there didn't seem to be anywhere to attach the lower block of your mainsheet..... it is possible that there is a piece missing from your backstay, the 20 at that time attached the lower block to a triangle plate about 12" up from the backstay chainplate, and the rest of the backstay attached to the top of that plate. (Theoretically, I'm not actually sure excatly when O'DAY switched to that setup from the original mainsheet rigging that had 2 blocks at the transom corners.) I have posted pics below to help, the O 22 had the same mainsheet rig as the 20, so even though the sketch showing the mainsheet attached to the backstay is actually from the 22 manual, it is still pretty correct.
I also noticed that you had a little problem with the spreaders?
I'll be at our Wareham cottage next weekend, you could also talk to Mr. Paul (I'm embarassed to admit that I forgot his first name!), but anyway, his son, John has a blue, 1975 Day Sailer II sitting in their yard (across the street from you?) at the moment, the family used to own a 1973 O'DAY 22 and He should be a good source of info if you see him.
For any parts (O'Day specific) that you might need, or for good advice, you can't go wrong calling Rudy Nickerson at D&R Marine in Assonet, MA. (508) 644-3001
www.drmarine.com . Rudy used to be the Parts Dept. Manager for O'DAY and now runs a little store selling (and making) parts for our O'DAYs. He is open for walk-in customers most Saturday mornings, and it is well worth a visit just to drool over his parts inventory.