Ok, I'm really remiss for not taking pics while I was at the boat. This is an unconventional wing mast, built using Gougeon Bros construction details, the clutch and swivel blk are nestled into a small enclave at the bottom of the mast, on the aft side, just enough room for these two pieces of hardware. The current clutch is secured with tow 1/4" machine screws, maybe 2.5" long, to T nuts embedded deep within the base, no access.
I'm currently leaning towards some method of securing the hlyd that doesn't rely on a clutch. With all this input, and a phone call this evening to Malcom, the builder, I'm contemplating a s.s. plate that can be drilled to use the existing mounting holes/hardware for the clutch, and attach the horn cleat to the plate. For raising the main, the hlyd can pass by the cleat to a stand up blk mounted to the main beam just below the mast, then athwartship to the clutch now also mounted to the main beam. This can hold the line as the main is going up, and when fully hoisted, release the clutch and secure the hlyd to the horn cleat.
But that's today's thinking, keep it coming boys! There may be better ideas out there! Thanks!

Dave

I'll try to post some pics of the boat.