Steve. , I am down to my last mast plug from the very reasonable ( Wolverhampton ? ) Dinghy Bits or some such name, who also seem to be low on stocks, a mast foot plug would be very useful. I have to grind the ones I buy as they sometimes are a tad oversize for the mast pot. I have at least one home made lower section requiring a plug. I have length of round hardwood stair rail which fits my boom sections nicely if anyone wants to try a local source, not as durable as yours Steve but they do the job.
I admire your ingenuity and inventiveness and craftsmanship in making excellent fittings. However as thousands of Minisailors used the cord or wire strop as standard to prevent undue loading on the luff incidentally and keep the boom above the measurement band and allow the cunningham to operate it is not unproven. The strop in non stretch line weighs next to nothing and and bowlines do not come undone under load. As our 1976 Minisail year book contributor from Newcastle confirmed, in another post recently. It also allows adjustment for slightly different luff lengths if one has more than one sail. Each to his own, but for me it's important not to invent more complex solutions to simple needs.