The crank sensor when indexed correctly makes the ecu see the ign trigger about 6 degrees sooner. So the base timing is increased 6 deg advanced. PM if you want more info or have specific questions.

The flywheel (trigger wheel) has 3 trigger indexes 120 degrees apart. The cam or phasing trigger tells the ecu if it is on the powerstroke or exhaust stroke to achieve full sequential injection.

The distributor engines use the same concept but a distributor button with a strap is used to give a good range for ign retard/advance.

 

Would it be worth looking at fuel trims with a cheap graphing scanner?

 

Anything scanner with live data and a decent refresh rate will do. I use an actron 9575. Its useful to see what the ecu is seeing from sensor inputs.

 

I see no one mentioned anything about the catalytic converter, if its not always down on power is this a non issue for the miles, Or is it worth replacing at this millage?
Im just trying to think of all options. I did a big Wyoming drive today and up a portion of highway i had a horse trailer pulling past me, saaaad lol.