This is largely a task for a professional spring workshop, but there is still plenty to do and learn about this topic.
First of all, do not follow the instructions in the AC handbook! Spring removal is awkward because the chassis passes underneath the axle, and the chassis underpan is below the springs. Firstly, disconnect the dampers (and remove them if they are the telescopic type). Jack the rear of the car up and rest the chassis on stands. As far as I can see, the only method for safe spring extraction, is to clamp the spring straight against some suitable girders. I managed to do this by clamping each half of the spring against separate short pieces of steel girder. The later version of this spring, has a very thick and straight bottom leaf, and you can use this to clamp the middle part of the spring straight. The spring will still jump up a little bit when you then remove a pivot bolt. For easy access, I recommend removing the rear seat and the aluminium panel beneath it. There are access hatches in the boot floor, spare wheel compartment, and also in the inner wings. Then remove the other pivot bolts and the U-bolts securing the axle. An alternative approach might be to clamp the front end of the springs to the chassis, remove the pivot bolts, and then release the clamp. However, you would need a clamp with a very long travel (over 5 inches/125mm) and one that won't slip off.
After releasing one spring, it is best to remove it completely before starting on the other spring, otherwise it will add to the stored spring load that you release on the second spring.
It is important to know the features of this spring design before taking it to have any professional attention. I often find that experienced trades-folk don't take kindly to be told what to do, so you need to be able to prove that they are dealing with something different!
When this model of AC was introduced, the rear springs had a free camber of 6.25 inches. A slight redesign was then hastily brought in, which had anunusual feature: A flat damper leaf added to the top. This leaf is straight when removed. When added to the spring, it reduces the free camber to 5.75 inches. Unfortunately, all the handbooks simply quote "6.25 inches". Unless you have a very early spring (without the flat damper leaf), then 5.75 inches is the required free camber. But don't let the spring workshop bend your flat damper!
Note that the camber is measured to the top of the main leaf, which is usually the 4th leaf from the top. Measure from a reference line passing through both pivot centres.When you have removed the springs, you should see gaps under the flat damper to confirm that its natural shape is in fact flat.
From reading workshop books, changing the Silentbloc bushes sounds straight forward. In fact, they are a very tight fit indeed. The workshop I took mine to, struggled to get them into to the springs and the shackles. So much so that they accidentally bent a shackle arm! After getting them to straighten it, I crack tested both shackles.
Outside diameter of the bushes is 1.00 inches, and inside diameter is 7/16 inch. Length of outer tube is 2.00 inches, and inner tube 2.125 inches.
The swinging shackles on my AC had a red fibre washer on each side of their lower pivots. The spring pivots had 1/8" (3mm) thick, soft fibre washers either side - probably made of asbestos. I couldn't find a modern equivalent, so I used 1/16 inch (1.6mm) thick, 1 inch red fibre washers in pairs. Unfortunately, I then realised that red fibre washers' inside diameter is smaller than the nominal dimension (1 inch) and so I filed them out to fit over the Silentbloc bushes. And to save too much fiddling with 16 washers, I stuck them together in pairs with gasket sealant.
Car restorers often seem to paint their leaf-springs. Unless it is for a show/concours car, painting leaf-springs is not normal practice. They are sprayed with oil during professional reassembly. I smear mine with grease to keep dirt out, and lubrication in. The series 1 and 2 AC handbooks mention regular cleaning and lubrication. The series 3 handbook says that springs were wrapped and packed with grease and require no attention. The springs on my AC were installed by AC circa 1960 and were not wrapped. Most leaf-springs to be found on commercial vehicles, railway vehicles, as well as old cars, were not wrapped, and I tend to prefer this approach. I painted the ends of my springs, to provide some rust protection, rather than risk getting oil on the bush rubbers.
If you have removed the damper subframe (for telescopic dampers), then note that it is much easier to bolt back on before the springs go back on the chassis. That's because the bolts are inserted from inside the chassis side rails, pointing upwards.
There is limited space for the pivot nuts, so make sure that your choice of self-locking nut will fit. Bolt the swinging shackles to the rear chassis fixing points, with red fibre washers, one each side. With the axle resting on the chassis, you can slide in a spring and bolt one end on (don't forget the fibre washers). If your springs have a straight bottom leaf, then be careful that it does not get hooked under the rear chassis underpan. Some folk put brake-fluid on the bolts, to avoid damaging the rubber bushes with mineral oil, but I use clear Waxoyl. This won't harm the rubber or the paintwork. Then attach the axle to that spring with a pair of U-bolts and new nyloc nuts (or all-metal self-locking nuts), with the spring-pad under the spring. Make sure the spring-pad is the right way round if it has a damper attachment (for telescopic dampers). Ideally, new U-bolts should be fitted, but I've been unable to find any that come even close to this size.
The next stage is to clamp the spring to some girders to straighten it as much as possible. Hopefully, you will be able to push down the other end of the spring by hand and get the last pivot bolt in (but those fibre washers are fiddly little rascals!).
Now you can do the same with the other spring, but its last bolt will go in easier because the first spring will help to straighten the second one. If the spring doesn't line up with the shackle, try turning the shackle around and/or slacken the U-bolts.
Final tightening of the 6 pivot bolts should be done with the normal static load resting on the springs. That is because the rubber in the Silentbloc bushes, deflects to accommodate spring movements (rather than having pivots in the literal sense). To minimise their deflection, you want them to have zero deflection under normal unladen weight. If the car is dismantled for restoration, then some ballast weight will help. Otherwise, make a note to slacken and retighten them when the car is reassembled.
Check that the U-bolt nuts are tight, and re-check them after running the car. The long length of the U-bolts, and friction between them and the axle, means that they can loosen soon after running the car.