"Check the engine wiring harness for deterioration,.."
I'd say that would be true of the spot where the engine harness wraps around under the front pulley---all 240s are vulnerable there but the '80 doesn't suffer the harness rot you see on later 240s up at the junction block and where individual wires exit the harness.
I've been driving an '80 245 w/M46 since 2000--had 123k then--around 280k now (since 275k odometer now works only when it feels like it). I've had no major repairs -- just the usual expenses for fluid changes, brakes, tires and exhaust. Heck, I only just changed the spark plugs a few thousand miles ago (see some previous thread for the reason).
It is almost the most boring car I've ever owned but it has taken me all over, towed other cars long and short distance, driven through the woods, carried scrap metal. It probably deserves a name but when I bought it the idea was to not get all involved with changing things to my liking and just use it like an appliance so it's just "the maroon wagon".
If yours is a stick shift check the firewall where the clutch cable comes through--they crack--mine has always been good. Check the differential cover--they rust through when old--later aluminum covers fit--JCWhitney has cheap chrome ones.
Check the struts for rust--just because they're 32 years old--mine are good.
The caveat to make sure the k-jet works properly is good advice--when they're good--they're very good--aside from changing the filters and the O2 sensor I haven't had to touch mine.
I don't baby my cars--when they're warmed up I'll use some rpm if it's called for. This car will "push" some oil with lots of around town driving -- maybe a quart in a month--but on the road NY to NC and back maybe less than a pint.
The '80 uses the outlet on the valve cover for the flame trap assembly. Make sure the flame trap is the later white plastic type rather than the original wound up brass strip.
32 is old -- make sure the heater works -- core not clogged (my valve is so stuck the cable adjustment is useless--pliers turns it on in the fall--off in the spring).
In a few of words--yeah, the '80 is a pretty good car. -- Dave