I would think that 5 stands would be about right for the K/CB model or the Fin-keel model (2 for each side, positioned to bear at points on the bilge that are at internal bulkheads, and one under the bow.) You will need 2-3 sets of wood blocks under the keel as well. On a typical K/CB boat, you may want the blocks postioned to allow the CB to be lowered a bit, which may allow you to at least partially clean the CB of growth.
I'm not sure what would work for your "swing-keel" model, since I've never seen a swing-keel O'Day (never built any that I'm aware of). However, a typical swing-keel boat would need a stack of blocks under the centerline of the hull just forward of and just aft of the retracted keel, plus blocks under the retracted keel itself, you do not want the heavy keel hanging only by it's lifting cable all Winter. The keel could also be just partly lowered to rest on the ground or a single block. You would then use the standard setup of 5 stands.
In any case, it is not out of the question to add a 6th stand under the stern for good measure, but not absolutely needed as long as the aft pair of stands are postioned properly.
You could check the Jamestown Marine web site for a link to the proper setup of stands or check any manufacturer of boat stands (Brownell is best known).
I attached a few pics showing the basic layout for a K/Cb model O'DAY 25, I assume that contrary to your description.... this is what you have?