The mast is in a storage barn (I've started treating myself to indoor spar storage ) so I don't know the diameter of the pin. I also recall it's fixed so I'll need to re-do it. But Rig-right has lots of options for what you have there in size as well as bolt diameter. Looks like it solves all the problems(as long as the floppy rings work as you say).

I'll run it by the sailmaker. I'll bet it's just what he would spec.

I'll miss the inverted U fitting that fits over the mainsail tack, fits into holes in the solid bronze gooseneck and is fastened with a rod that fits through notches in the U, and threads. It's easy to use, sure, and built to last for several life times, brilliant design and craftsmanship, now retired.