I might be way, way off, but here's my take on it:
The aka is 13'4" (160") long and I am guessing an average of about 4" wide and deep (taking the rake into account). So that's 2560 cubic inches, which is 213.33 cubic feet of water displaced by an ama.
I'm afraid you've only divided by 12; you need to divide by 12^3...
2560/1728 ci/cf = 1.48 cf. 1.48 cf * 62.4 lb/cf = 94.2 lb. I think the 4" depth is a little conservative so the actual buoyancy is probably a bit higher.
If you ever see your amas in a substantial wind, you'll wonder how much more wind before it fully submerges. At that point, there's so much drag from the amas and required rudder (which is near it's limit) that it's silly not reef.
Even if you push to amas buoyancy limit, the amas is being pushed through water, as opposed the the windward cat hull that is being pulled through air.