After you follow the suggestions above; I agree about getting the boat light. After completing the initial suggestions, I'd get her empty, very little water
, empty, and take her out, see what you have. You probably will need to do this several times. This would be my assessment sail weight. If I was pleased with this results then I would begin to load the boat carefully and monitor
the changes; when sailing performance began to suffer you will know you have reached payload.
If after the initial "empty weight" sailing evaluations you believe a board would make a difference I would consider a swing board located in the main hull, with a box built under the long salon
bench. Boards in the main hull do not need to be centered or another way to look at it is they can be off center and still be effective. However if you can figure a way for a dagger box in the main hull that might even be better.
Take a look at what Chris White did in the Hammerhead 54 Chris White Designs
Shannon has put a dagger boards
port and starboard of their new 53HPS monohull http://www.shannonyachts.com/sail53specs.html
I think this would also be less stressful on the boat as compared to the boards in the amas.
If I was going to add flotation I would think about only adding it to the amas and use something like this:
You would need some type of internal decking at or perhaps just above the waterline in the amas to pour the foam through so it would form and contour to the hull shape below; the decking would be the upper part of the mold
and contain the foam in place.
I hope you will keep us informed and let us know what you do and the results.