Howdy Back CUL8ter:
First, check on the EPA rules in your locale. Even though the EPA is a federal deal it is applied and enforces by states and locales.
You are somewhat stuck if you must maintain all of the stock EPA stuff on the '81 engine. The stock ignition system in good shape is about as good as it gets for economy. You can increase the initial timing by about 5 degrees over stock specifications. Adding the MSD box and/or a hot coil may improve starting and idle, and performance above 4,000 rpms, but it would take many, many miles to break even on the cost due to increased mileage. You'd probably do better airing your tires up another 5lbs and driving 5 mph slower.
The hurtful application of the EPA requirements when your car was new are that the exhaust is very choked off, the cam timing is retarded and the carb is one of the most limited and feed back, electronicified of any carb ever. A new high flow catalytic converter and high flow cat back exhaust system would help. The cam timing can only be solved by changing the cam gears and chain to an earlier, straight up set. The Holly #1946 carb can be improved upon, but only by undoing and eliminating the EPA systems which may be illegal for you. Again, check your laws. Often for a car this old and an engine with many miles, the rules may be more liberal (dare I say that word on this forum?).
When it's time for a valve job, you will have several opportunities to improve economy and performance. In 1981 these were unnecessarily low compression engines. Raising the compression to the neighborhood of 9:1 will help economy a bunch. It will probably be the most cost efficient single thing you can do. In addition to milling to raise CR, insist on a three angle valve job, back-cutting the intake valves, and consider installing an exhaust port divider.
I hope this is what you were looking for.
Adios, David
