MSD or Ac Delco

The benefits of either new to new are negligible assuming you use the same style of plug wires. They are very similar, you are just paying for the MSD name (unless you plan on adding an actual MSD ignition box for true multi-spark). I have not tried a compete dist swap yet but that might have benefits over the AC Delco. With 198 k miles I would recommend complete replacement or at least change the pick-up coil and ignition control module as these are the major points of failure on the TBI engines. If your looking to improve economy it's the TBI system that will help the most. OBD1 is limited for tuning options but there are some. A OBD1 live scan tool or an ALDL cable helps a lot with sensor errors as there are a few issues that cause low mpg without flagging the check engine light.