This is a VERY simple conversion to install the late model large distributor cap onto an earlier model engine. The subject truck is a 1976 with a 390 FE motor. It has the stock small distributor cap and matching spark plug wires. The reasons for doing this conversion are:

1. Reliability. The terminals are farther apart in the large cap and this helps prevent cross fire in the cap. The larger wires also conduct better.
2. Performance. The larger separation in the cap will allow the use of more powerful coils without cross fire.
3. Appearance. The conversion is clean and looks very trick.
4. Why not?

You will need to pick up 4 parts:

1. Spacer. This is the adapter that allows the large cap to be used. The large cap is actually flat and snaps onto the spacer. This can be had at a wrecking yard cheap.
   
2. Cap and Rotor. Matching set, get one for a late model 302 or 351W. Can be had at the wrecking yard if you can find a good set.
3. 8.5mm Spark Plug Wires. The larger cap will only work with the larger wires so your old wires won't fit. If the donor vehicle has a good set snag them.

You will notice that all parts can be had at a wrecking yard if they are in good shape. This may not be too far fetched because some people will give a dying car a tune up to try to keep it running and when it does die the new parts go to the wrecking yard on the car. There are tune up kits that include the cap, rotor and wires but normally the spacer is not included so that is the only one you should get at the wrecking yard.

Installation is straight forward:

1. Note spark plug firing order and write it down!!
2. Remove the old distributor cap and rotor.
3. Install the new spacer. There is a rubber plug in the base of the distributor that will cause a little interference. The spacer has a square tab that fits in the cut out that the rubber plug is in. The plug can be compressed by the spacer so it will fit or you could trim the plug. I don't recommend trimming it because you could cut the wires that go to the magnetic pickup. See the arrow in the photo.
4. Secure the spacer in place with the snap springs that held the old distributor cap.
5. Install the new rotor.
6. Install the new cap.
7. Install the 8.5mm spark plug wires.
8. Step back and enjoy your handy work.