First of all look at the rear end - is it lower than it should be? Of course this may be due to tired rear springs (see here) but it may also be the body having collapsed around the rear mountings. Have a look at where the rear overrider supports come through the body. They should be in the centre of the holes in the body. It they are high in the holes or perhaps even touching the top of the holes then the body mountings have sagged. It is not surprising that should happen as the design of these mountings leaves a lot to be desired. You will find them inside the boot just behind and inboard of the wheel arches. Yes, I mean those rusty lumps with a bolt head in the middle. They are far too far forward to be good rear body mounts especially with the very heavy spare wheel bouncing up and down just behind them. What is needed is another set of mountings further back to take the weight off them.
It is easy to make up and fit an additional set of mountings. Look under the car and you will see a cross member in the shape of an upside down U section running between the front end of the rear jacking points. Its obvious function is to support the rear of the petrol tank but it can easily be used to support the rear of the body too. Just above it is the floor of the spare wheel compartment where all the weight resides. Lift the rear of the body with a couple of jacks until the overrider support irons are central in the body holes and then raise it just a smidgen more. Measure the gap between the spare wheel compartment floor and the cross members and make a couple of hardwood spacers so that they slide into this gap either side of the petrol tank mounting. They should be a couple of inches wide and as long as possible. Now drill a couple of holes in the cross member for each of the spacers so that they can be held in place on the cross member with wood screws. With the spacers firmly held in place lower the body off the jacks and the job is almost done. Finally remove the spare wheel, drill right through the cross member, each of the spacers and the spare wheel compartment floor and clamp everything together with long bolts. Coach bolts are probably a good idea as they have smooth domed heads which will not catch on the spare wheel as it is slid in and out.
Now that didn't take long did it? The rear of your car should now be in the correct place and you can forget about those rust lumps in the boot and the way the body used to clang over bumps.
With that success behind you have a look at the doors. Are there large gaps between the front doors and the frame near the top of the windscreen? If there are then the pillar (B-post) holding up both doors has dropped. If you look under the running board by the door pillar you will see a body mount and it will look as if the packing is made from chipboard which has seen better days. It is very easy to assume that releasing the mounting bolt, jacking up the body and using a thicker piece of packing will overcome the problem. Well, it might for a little while. The real problem is not the packing but the design of the mounting. Look where the mounting bolt comes through the floor in relation to the door pillar. The pillar overhangs the mounting bolt and hence the chassis mounting by far too much. With so much weight carried by the door pillar it twists the wooden floor board downwards. The floor board might have been able to withstand this when it was new but fifty years later it is asking a bit too much. Once again we need to give the mounting a bit of help.
To make life easier, take out the front seat by removing the safety screw and sliding it backwards off the runners. Lift up and pull off the trim covering the inside of the door pillar and pull up the carpet. You can now see the body mounting bolt and the wooden floor. Look at the floor carefully and you will see that it slopes downwards from the body mounting bolt towards the bottom of the door pillar. That's where the real problem lies. Before proceeding further make sure that you have a short length of heavy (about 3/8 in. thick) angle iron which can span from the door pillar to past the body mounting bolt hole and a welder (arc is fine). The angle iron need only be as long as the door pillar is wide as we are going to use it to extend the bottom of the door pillar inwards to sit on top of the floor and to reach the mounting bolt. Now jack up the door pillar to take the weight off the mounting and remove the old mounting bolt. Jack up the door pillar until the doors fit properly. Now lay the angle iron on the floor and against the door pillar so that it covers the body mounting bolt hole. Tack weld the angle iron to the door pillar. Just a small tack will do as you do not want to burn the door trims. With the iron held in place, open the doors wide and weld the iron firmly to the door pillar. The idea is that in future the angle iron will take the twisting load and not the wooden floor.
With the iron welded in place, shut the doors and adjust the jack until they fit properly and now make up a new hardwood spacer to replace the old chipboard one. Carefully lower the jack and let the new mounting take the load (remember it has not been bolted up yet). Check the fit of the doors and adjust the thickness of the new spacer if necessary. If all is well, drill a new mounting bolt hole up through the spacer and the angle iron and fit a new bolt. The job is almost finished.Finally replace the carpet, the door pillar trim and the seat. You will probably have to cut off a short length from the bottom of the wooden filler inside the door pillar trim to allow for the welding but this will not be visible when everything is in place.
Next time you take your car to a Riley meeting and people notice that the back of the car sits higher and squarer and the doors fit better, don't tell them our secret. Just tell them that you replaced the boot floor and the floor board cills. We know that it took a weekend but let them think it took all winter!