The key is to get the mast jack to work as a jack, that is to get the bronze nut to turn. Once that works, attaching fixed length stays should be a snap, because they are not under tension until the mast jack is jacked up.
From a previous owner I inherited a small home built contraption that makes stepping a keel stepped mast almost as easy as using a tabernacle. I've written about it extensively, here in the forum and in a writeup.
You may want to look up the past discussion.
Like a tabernacle, it uses a hinge, but it's not part of a divided mast, but external, so the mast remains keel-stepped. With it, I regularly step and unstep the mast by myself while standing in the cockpit.
Here are a few pictures as a teaser:
![2744](./gallery/image.php?mode=thumbnail&image_id=2744)
![1545](./gallery/image.php?mode=thumbnail&image_id=1545)
![2679](./gallery/image.php?mode=thumbnail&image_id=2679)
The construction is dead simple and requires no advanced skills. The mast end is inserted into the sleeve, the mast is lifted into the vertical, and when it's aligned it can be lowered through the deck (it won't go in unless it's pretty well in alignment). With practice, I can hit the mast jack pin blind, but the mast is held well enough that you can even risk bending down for a quick peek, if you missed it.
The whole thing is attached to a disk made from aluminum that is bolted around the mast partners (the opening in the deck). That disk can be used to attach fairleads and other useful things w/o needing to drill the deck for each fitting.
You can see the disk, the cluster of 4 bolts close to the mast that hold it, one of the fairleads (black) which I use for things like spinnaker halyard, and the simple hinge, the wooden block to which it is attached, and the bit of aluminum sheet metal that forms the sleeve itself. That's basically it. (There's a T strap to help support the attached block against twist, and, not shown, a bit of material that fills the gap between deck and disk in the front to keep out the jib sheet. Refinements I added over the years.)
I also added a U bail, seen in some of the pictures, to attach the vang. (The sleeve is strong enough to easily withstand the pull from the vang).
A more complete description can be found under "raising a keel-stepped mast".