There are three main pieces: the ceiling mount, the sliding arm, and the plastic (polycarbonate, Lexan) guard. I also added a splitter that works rather better than the flimsy ones that come with saws that makes it very hard for a board to catch the back of the blade and get flung back at the operator. The ceiling mount is just a couple of pieces of the arm sandwiched between two pieces of 3/4 ply. This makes a channel for the arm to slide up into. This is glued and screwed to a 3/4 plywood plate that gets screwed into the ceiling joists. I was going to put cross bracing on it, but it is solid as a rock, so I didn't.
The sliding arm is quarter saw ash, but any straight grained hard wood would do. This is made of two pieces; the top slides into the ceiling mount and is held fixed with a pin made from a 3/8 inch diameter eye-hook and wing nut. This makes it easy to remove. The bottom arm was ripped down the middle and 3/8 inch wide pieces of cherry glued in to make a 3/8 inch wide slot down its middle. Two 3/8 inch diameter carriage bolts are mortised into the fix upper arm. They go through the slot in the lower arm, and when loosened, they allow the bottom arm to slide up and down. The top bolt has a washer and jamb nut, jammed with a wing nut, just loose enough not to hold the sliding arm in place, but tight enough to allow almost no play. The lower bolt is tightened with a washer and wind nut. The lower bolt has the job of keeping the arm fixed in use. Just loosen the bottom wing nut to raise or lower the guard. The threads on the bolts are sharp and make it hard to slide the arm, but a few licks with a file fixes that.
The last thing is the guard itself. This is a Lexan box, made with 1/4
inch thick Lexan. That seems a little thin, but is thick than the stock
blade guards, so should be ok. I glued the box with super glue, but getting
a hot air gun and bending it into shape would make it stronger. There is
a 1/2 inch Baltic birch plywood piece screwed to the bottom of the lower
arm, and the guard is attached with, I think, number 10 machine bolts,
again with wing nuts. The bolts go through slots in the cross piece, so
the guard can be adjusted left and right.
You can see the splitter in the last picture. The throat plate on this saw is only 1/8 inch thick (give or take a few thou). Making a fully wooden one bothers me, since it would have to have an 1/8 inch thick lip all the way around, and that does not sound strong enough. So, what I did was to drill and counter sink two holes (actually one was already there) near the center line. Then a 3/8 inch to 1/2 inch thick piece of wood gets screwed underneath. A thin piece of wood is ripped off the edge of a board and trimmed to drop into the original opening in the plate. This is glued in the slot. To cut the slot the plate is put in flipped end for end (the blade hits the wood underneath until a kerf is cut into it) and held in place while the running blade is raised up through the plate. Now the thing is flipped end for end again, back the way it should be, and the blade raised again. This has the result of cutting a kerf well behind the blade. Now glue in a thin piece of wood in the kerf that extends into where the blade will be. I use a piece just ever so slightly narrower than the blade so it can not hang up the board as it passed. Glue into the slot (with a very thin shim if needed to get a tight fit). Now raise the blade a third time to the height you want. This one is good for boards up to a little over an inch thick. The narrower the range of thickness you use the splitter on, the closer you can keep the splitter tucked behind the blade. As you can see, it would be very hard for a board to slide over and get to the back side of the blade.