John, I got a few replies, but these 2 agree with what I suggested (others thought shrouds chainplates or unknown):
"I am certain Dan Reiber would know. It seems they are for a lifting bridle to transfer the boat from the land to the lake and reverse. The boat’s center of gravity is located in the same area between the two fittings. There are chain plates on the inside with fasteners through the hull To support the weight. Each fitting only has to handle about 125 lbs., and am almost certain that when hiking out in a stiff breeze where the shroud is taught, there has to be more force exerted than 125 lbs. for a comparison." Bob Corpstein, J1952
And Dan Reibar agreed: " Bob’s description seems accurate to me." Dan Reiber
If I hear any more ideas, I'll let you know. However, it seems like the lifting bridle idea is leading!