Ballast or foam?

[spooky alice]

I have a 1975 Reinell 22 ft sailboat. I've been chasing a small leak which lead to installing 4-6" inspection ports in the sole of the cabin. these were to look for water and the other to keep a eye on whats going on below the floor in the shoal keel area. What I found was very little water but some rather large open cavities. I'm wondering if this would be the time to add some extra ballast or fill with foam, or just leave as is. There is no wood I can see to worry about so any water retension by the foam shouldn't be a problem.The boat doesn't have a bilge pump and I thought about adding one in this area, but don't know if it will work as the discharge would be about 3 feet above the pump and plumbing would be a real challange.
My thoughts are if I add foam, I can get into foamed areas in the cockpit area and remove foam to add a storage hatch and keep my floatation the same.