[benz]

Thanks Brion,
I figured my plank idea had to have a nautical name. Channels...I like it. I've certainly considered using a standard mast section with a track, but yet another reason I'm going with a gaffer (a pretty small reason among many others, though) is that I dislike track slides and cars and all that paraphenalia. And mast sections are expensive. I made a full-size model of the bit of mast where the shrouds attach and the gaff sits, out of a bit of stovepipe and some ropes, and put a model gaff jaw against it to see about the swing (I have to do things that way; not good at scaling or theorizing), and I'll dust it off and try it some more with different peak angles.
Ben