I recently upgraded to 22mm front torsion bars and 29mm rear bars. Here's a quick rundown on the procedure.

Before you do anything, clean all the grease and road grime off the rear suspension to make the job nicer and easier.

I hook a hose to my hot water heater, crank the temp all the way up, and give it 1/2 hour or so lead time to come up to temp.

Spray on some degreaser - I use Castrol SuperClean

Let the degreaser sit awhile to soak in, then hit it with the hot water.

Ah! A nice clean suspension to work with! Put the rear of the car on jackstands, and remove the rear wheels.

Remove the torsion bar cover plate in the body - you may have rocker trim which must be removed first on your car.

Here's a look down thru the torsion bar access hole.

Remove sway bar drop links

Remove the lower-rear torsion cover bolt and spacer - this lets the torsion bar drop completely and avoids any tension on this bolt. (17mm wrench)

Here's the spacer removed - leave the other 3 bolts in for now.

Here's what the bolt and spacer look like - put this in a safe place and don't lose it!

Use the jack to support the trailing arm, then remove the lower shock bolt. You'll have to lift the trailing arm slightly to relieve the pressure on the bolt. If you don't support the trailing arm, it will come down in a hurry when you remove the bolt. (24mm wrench)

Here you can see how much the trailing arm comes down after you remove the shock bolt

Remove the 2 trailing arm bolts (19mm wrench)

Remove the adjusting bolts (19mm wrench)

Spring plate free of the trailing arm

With the spring plate freed of the trailing arm, take a measurement of the spring plate angle and write it down. You'll want this measurement for later to guide you in setting the new ride height.

Closeup of the magnetic dial protractor I use - these are $5 at Harbor Freight tools

This is a nasty surprise I had waiting for me - a torn sway bar mount. This is common on the early cars, and is made worse when you put big sway bars on a car with soft torsion bars.

Remove the remaing 3 bolts, then pry the plate off with a couple of large screwdrivers

Here's a shot with the cover removed

Remove spring plate by prying off with a couple of screwdrivers

Plate removed

Slide the bar thru the access hole. You may need to grab it with a pair of pliers and a rag.

Use a wire brush or wheel to clean any rust or leftover rubber in the spring plate cover, and in the torsion tube, if necessary.

Here's a comparison of the old torsion bar (red) and the new one (white)

Here's the different ends of bars; note the different numbers of teeth.

Use a rag in the access hole to protect the paint on the torsion bar

Smear grease on the bar on the bar as you slide it in, to protect it from any moisture that may get into the tube.

Remember to center the adjuster if you have adjustable spring plates

Here's the special ride height adjustment wrench needed. With the spring plate removed, a normal wrench would suffice, but you won't be able to make adjustments while plate is on the car with a normal wrench.

This is a good opportunity to install new spring plate bushings. I'd installed mine last spring. I used Neatrix bushings. The OEM bushings are only available with new spring plates, as they're bonded. I used an air chisel to remove the old ones, which is probably the fastest, cleanest way to do it.

Push the spring plate on.

Raise the trailing arm with the jack to get it out of your way

Make your first attempt at setting the ride height. You must set the angle with the trailing arm disconnected and the spring plate unfettered. I tried to make an educated guess about where the initial setting should be; the old angle was 29.5 degrees...

Or, you can use my spring plate angle calculator

I tried 26 degrees, and it was too high...

Then I tried 16 degrees - a bit too low... I ended up at 22 1/2 degrees - the spiring plate angle calculator gives 22-23 degrees. To adjust the spring plate, you'll need to rotate the inner and/or outer splines one or more degrees. By moving the inner a certain number of splaines and the outer an certain number of splines in the opposite direction, you can achieve a small incremental adjustment. For example, you can move the inner 2 splines and the outer 1 spline to get a tiny adjustment, or move the inner 1 spline and the outer 1 spline, to get a larger adjustment. Adjusting to a steeper angle (spring plate lower to the ground) raises the car, adjusting to a shallower angle lowers the car. The trick to moving one spline at a time is to pull the bar (or spring plate) out very slowly and carefully, while applying a slight amount of torque (rotating pressure) in the direction you wish to turn. When the male splines are free of the female splines, you'll feel the 'give' - which is why you don't want to twist too hard. Then, rotate the bar while pushing in with a small amount of force. When the next spline lines up, the bar will fall in.
I 'cheated' by choosing a setting, then installing the 2 rear trailing arm bolts (and not the adjusters) and installing the shock bolt, then letting the car down hard - be careful! This let me try more iterations in a short period of time, but I had to let the car down hard and fast or the suspension wouldn't take up the slack. This saved a lot of time in installing the adjusters and cover plate over and over.

Put the spring plate cover back on - this takes some patience, as you'll be fighting your new bushings to get the bolts started.
Once your ride height is set, it's just a matter of bolting everying back together and putting the wheels back on. Take a short test drive to set the suspension so you can verify your ride height is really what it should be. Mine was a little higher than I wanted, but I was able to drop it to my liking using the adjustable spring plates.

Here's how I fixed the torn sway bar mount. My car has the original mounts, and it appears that one of them broke at one point, so someone had tried to reinforce them with a piece of angle iron. The new larger sway bar was too much, and ripped out one of the mounts.

Closeup of the damage

The lower spring plate cover nut also had a crack around it

I also had a split in the seam, but this was my fault - I'd been putting the jackstands here. Not gonna do that any more!

Here's a closeup of the tear in the lower mount area

Here's my welding of the tear - welding upside down is a pain! I added a piece of flat stock to further reinforce the mount

I also tied in the old mount to the angle-iron reinforcing piece better. I think if they'd done that originally, it wouldn't have been as much of an issue. I also welded it on the inside but I couldn't get a clear picture.

Welding up the crack around the nut.