Since your truck is an '82 it will already have HEI installed. If the stock plug wires are in good condition its unlikely to see any gain by changing just the wires. A performance coil and wires will help a bit. MSD has a multi-spark ignition module that fits inside the HEI dist. Where you will notice a difference is at idle and cruise.
If you really want to pickup mileage then the next 2 steps that will help is:
1) installing an overdrive transmission
2) installing TBI fuel injection
But both of these invlove more $$$ and at the end of the day its upto you to decide if the extra parts are worth the expense or just pay at the pump. With the OD and TBI you can expect a 15-25% increase in fuel milage.
