Welcome - Nice looking 80
If I were you, I'd dump the K&N filter and return to stock OEM. There are a few threads on MUD discussing this. My 80 came with a K&N and when I changed it out with OEM I posted up some measurements etc. to MUD. Some people love them so to each their own.
As for the rest, sounds like you have good records so start with a good baselining of the fluids, a tune up, and go from there