Select two anchor points forward and aft of the mast step, usually on the gunwale or side decks, on each side of the boat. (I have seen 2 lifeline stanchion bases on a Precision 21 used for this.) Use stranded SS wire with Nicopress swages or splice some single braid Dyneema lines to a carabiner of your choice to attach to the mount points. Splice the other ends to a welded SS ring. Adjust so that this bridle sets the welded SS ring at the same relative position (fore/aft and height) as your mast step pivot point. (I have also seen this done with line tied to the carabiners and ring.) Then attach baby stay line to the ring, and carabiner of choice at top of baby stay. Baby stay attaches to tangs riveted to side of the mast. They do not need to be too high on the mast, in fact, make them low enough to easily reach up and unfasten the carabiner once the mast is stepped.
Custom setup that will not slack as you raise or lower the mast. Makes it easy peasy!
I have also seen folks attach baby stays between top of gin pole and SS ring. If you affix the gin pole at the mast pivot bolt as outlined above (great idea by the way!) then the gin pole will also pivot in the same place as the mast and the SS rings, so the baby stays on the mast and gin pole will not slack, and will hold the whole shebang straight as an arrow. If I had to routinely lower the mast on the water, say to get under a bridge to get to sailing water, this is how I would do it.
Some people use the vang or mainsheet for the multipart purchase to lift the works. Having a multipart purchase with a cam cleat that grips the line is a great idea, you can partially hoist, and then stop, and go futz with out of alignment turnbuckles to your heart's content, and not worry about the mast coming back down.
