Since I happen to like the Mac26 concept, I
wonder if it can be modified to be seaworthy.

are you ready to reinforce the entire hull, the entire deck, the hull/deck
joint? are you ready to replace the mast, boom, standing rigging and running
rigging with gear of appropriate strength? Are you willing to pile a couple
thousand pounds of lead low in the boat to improve its stiffness and limit of
positive stability? are you ready to replace all ports and hatches with gear
of appropriate strength? Are you ready to replace all the winches? are you
ready to build in internal bulkheads to reduce hull twisting in a seaway?

seems to me to be a lot like trying to turn a Yugo into touring sedan.