Not an O’Day owner but the information you seek can be found.
Checkout this data source.
Complete Sail Plan Data for the O'day 302 Sail Data. Sailrite offers free rig and sail dimensions with featured products and canvas kits that fit the boat.
www.sailrite.com
Where the size for the ODay302 asymmetrical is specified.
Rigging an asymmetrical is also available as the 302 is rigged pretty much the same as a Catalina 30 or a Cal 35. Or pretty much like every mastheadsloop made.
You need a Spinnaker Halyard preferably on a mast Crane.
A tack sheet that can be run to the cockpit to adjust.
Finally 1 or 2 sheets to control the sail. These run outside all of the rigging to the stern. Then you turn the sheets into the cockpit using a block. You secure the sheets using a cleat or a clam cleat.
Enjoy the sail. They are a lot of fun.