This is definitely a worthwhile modification and is pretty easy to perform as well. Obviously before carrying out this work though, you'll want to clean out the wheel arches of your car and make any necessary repairs as well as ensuring the stone-gaurd/underseal coating is in good order.

You will need:

From MK4 Escort/Orion

One pair of wheel arch liners.

8 Plastic plug nuts (as found behind the liners)

NEW

10 Self tapping screw and large penny washers

Small section of steel

Heavy duty sealant or thick underseal

The first task is to go to your local breakers and get the required parts. Any MK4 Escort/Orion will do, there all the same. Remove the self tapping screws and plastic turn clips that secure each liner in position and withdraw the liners. Once removed, you will see a number of white plastic discs about the size of a 10pence coin on the inner wings. These are the plastic 'Plug Nuts' that the self tapping screws go into. Leaver these out and retain them. You'll now need to remove the liners from another car in order to obtain more of these plug nuts as you'll be using these and self tapping screws in place of the plastic turn clips when you come to mount the liners into your MK3.

Back to your car. You will need to apply some form of heavy duty sealant to the inside of the return lip on the fold of the arches on the outer wings. This is because on the MK4 cars the return fold has a tang built in to locate the liner (as you'll see when you come to remove the liners from the donor cars). As this tang is missing from the MK3 wings, the liner will have a tendency to rub back and forth slightly and so chafe. The sealant will both act as a barrier and help grip the liner to reduce this movement.

Once the sealant or underseal has dried, fit the liner in place using the steering arm and drive shaft cut outs as a guide to positioning. Once you are happy with the fit, mark out the liners mounting hole positions on to the inner wing of your car with paint or similar. You will find that the top row of holes are sitting in space, don't worry about this, it's not going to cause any problems. You will however need to seal these holes up with something such as grommets to stop dirt and road spray from passing through them.

Remove the liner and with the exception of the lowest hole position below the steering arm, drill the centre of the marked hole positions with an 8mm drill. These holes now need opening up with a file to produce a rectangle hole of sufficient size to house the nut plugs. Prime and top coat the edges of the holes and once dry, push the nut plugs home with a smear of underseal for good measure. The last hole is to be drilled a suitable size to accept the self tapping screws. The reason that a nut plug is not used here is that it is in a stress location and a rectangular hole here will induce cracking. Re-install the liner and secure with the penny washers and self tappers, check for location.

The lower rear mounting hole is also sitting in space and for security of mounting, could really do with being attached to something. For this, a simple 'L' shaped bracket needs to be fabricated and welded onto the shell. The bracket should be bent to approximately the correct size and offered into position with the liner in place. Mark the bracket where the hole lines up. Drill and file this hole as before to accept a plug nut and attach in position. Then mark the shell where the bracket needs to be mounted. Thanks to the large size of the holes, you have a little movement to play with. Remove the liner and weld this newly manufactured bracket into position. You should find it lines up nicely with a large flat as shown below. Refit the liner giving the lower self tapper a good coat of grease to prevent corrosion and bobs your uncle!