I think, based on what I heard from a former VP of O'DAY (Robert Pierce), that they used lead "ingots" shaped to fit inside the keel, which were then encapsulated in resin, at least that was how they built the 23-2, so I would assume the 22 keel was same. The reference to lead shot in resin would have been that O'DAY suggested owners use that method if they wished to add more ballast to their 22. The lead shot could easily be poured in through the small inspection/bailing hole in the cabin sole ,then resin poured in to keep it in place.
Rudy Nickerson (D&R Marine) would know how the ballast was installed, he was the Parts Dept. Manager for O'DAY from 1973-89 and now supplies us with spare/replacement parts.
From the O'DAY 22 Manual:
Bilge Drain Plug:
The plastic plug in the cabin floor located over the aft end of the keel is provided so that any water in the hull can be pumped out. Be sure to check this area prior to sailing.
Ballast:
The O’Day 22 has 600 lbs. (1972-78) of lead ballast glassed into the keel, which is more than adequate; however, you can add more, if you prefer more stability. The easiest way to add is to pour lead shot (available at any good sporting goods store) into the keel area through the bilge drain plug. You may even mix with catalyzed resin for a more permanent job, but be sure area is dry. We have customers who have added 200 lbs. In this manner, but be sure to increase positive flotation at the same time in order to support the extra weight, should the hull take on water through a leak or hull puncture.
(Ballast was 700 lbs. for 1979, 800 lbs. for 1980-83.)