The front bodywork needs to be dismantled and this is bolted together. You might need to hacksaw through some or most rusty bolts. The AC uses a lot of little UNC machine screws and nuts, which American readers will recognise as size 10 (or 10-24). This size is roughly 3/16" thread diameter. You can break rusted examples using a hammer and chisel. The steering wheel and column will have to be removed before the aluminium part of the bulkhead can be detached. The wiring for the steering column is fitted through a removeable tube which is fixed at the bottom of the steering box with a coupling nut and an olive (these seal in the steering box oil). On the steering wheel, there are some grub-screws that need to be slackened before the horn button assembly and wiring can come away. The steering wheel is fixed with a heavy duty circlip.
The rear wings are fixed to the wood frame with large woodscrews. These might pull out if the wood is very rotten. Or else you might have to force the aluminium washers off so that you can grip the screw-heads with pliers. If you're lucky, they might come out with a screwdriver! The steel inner rear wings are nailed to the wood frame. UNC machine screws pass through the inner wings and boot side panels, to support the boot floor. Bolts pass through into the chassis side rails. The chances are that the inner wings have rusted away sufficiently to make removal very easy!
Interior trim has to be stripped out. Remove the seats and the varnished wooden trim and cappings. The roof edge trim can then have its cloth raised to reveal the card underneath which can be prised off the panel-pins holding them. Then the headcloths can be carefully removed starting at the front, and removing the tacks - lots of them! The leather covered door trim panels have long nails holding them to the bottom of the doors. The main floor carpets can be lifted to reveal hidden tacks along the edges nearest the doors. Other carpets are either tacked to the wood frame, or else 'glued' with bitumen. The floor panels are fixed with a mixture of woodscrews and 10-24 UNC screws.
Remember to take plenty of photos at every stage so that you know where everything goes.
My AC's wood frame was largely sound and strong/rigid, but if yours is falling apart, then you might need to make some temporary framing to help support it, and to make sure that it is not sagging or leaning to one side. If your wood frame has all but disappeared, then you may have to work largely from panel dimensions and build a wood frame from scratch. The steel brackets that reinforce the door hinge pillars, should help provide a reference for major dimensions of the body. The position of the front inner wings and alloy bulkhead might also provide a guide to where the plywood part of the bulkhead should be positioned.
If you are going to do the full restoration and remove the bodyshell, then this is where it gets more worrying! The bodyshell was not designed to be removed, and was originally fitted in a number of sections which were then welded up in situ, leaving slight scorch marks on the wood. Even so, many of the edges of the panelling would have been hammered over the wood frame, such as the rear and side window surrounds.
To remove the bodyshell, you have to unfold some of the edges. The most difficult edges are arround the rear and side windows, since the curvature means the panelling creases. You need to unfold it just enough to be able to lift the bodyshell off. The rear half of the wheel arches needs the edges unfolded, and the same along the screen pillars. Other edges do not need unfolding as they don't obstruct lifting off the panelling.
I used a very wide (3/4" or 19mm) screwdriver blade that was sharp enough to prise up the panel edges, but wide enough not to dent the wood. Most of the panelling lifts off the panels pins which can be pulled out later. Note that when the panelling along the door-steps is freed, it is very easily damaged and if you need to move the car, I suggest you tie these panels so that they don't stick out. The freed bodyshell can be lifted easily by two people. It is light for its size, but needs two people to handle its large size. Before lifting, check for cracks at the ends of the two strips across the rear end of the car. These crack at the welds, but if they are not cracked yet, they might split while moving the bodyshell. Either way, it might be a good idea to clamp some reinforcements onto each weld. I suspended the bodyshell in my garage over the rest of the car, by resting the rear end on a pair of wheels, and the front end on a wooden frame that I made for the job.
Most of what I hear and read about working with aluminium alloy panels, suggests that it will crack to pieces if you even think about bending it! I know that some small areas on my car had dents knocked out years ago, and the little detachable wing panels had the edges unfolded and re-folded without annealing. I wouldn't recommend bending things so many times without annealing, but it has demonstrated that these panels can survive more work-hardening than expected, before cracks appear.
With all the photographic and dimensional data gathered, the next stage is to make sure that the shape does not alter once you start to remove wooden components. Firstly, the frame needs to be supported correctly so that it is not twisted. If you have the space and equipment, then transferring the frame to a wooden flatbed might be an option. Personally, I think this is risky unless you know what you are doing. I prefer to keep the frame securely bolted to the chassis until it is fully repaired. This approach also requires some care. The rear of the chassis can twist fairly easily, so make sure the car is on flat ground and that all the springs are settled (if the axles are still fitted - which I prefer since it keeps the chassis loaded roughly as it will be when finished). That is, leaf springs have a certain amount of static friction, so stand on each corner of the chassis and press it down. Then check by sight that there is no twist along the chassis' length.
The next stage is to make wooden alignment jigs (unless these were done at an earlier stage on a frame that was falling apart). These will support areas of the frame while you remove any major components. The jigs will need diagonal bracing to keep them rigid and prevent any part of the body frame from sagging, twisting, or shifting to one side.
As repairs progress, the shape of each part and assembly should be checked against doors, windows, wings and inside the main bodyshell as appropriate. If major parts have been removed and refitted/replaced, then also check that the frame does not lean to the left or right. Diagonal measurements across the width should be equal, but allowing for the fact that the two halves of such a car are not exact mirrors images - having been hand made.