1986 Mercury Marquis Won't start

Hello, I have an 86 marquis, 5liter. I can't get it to start. I've done everything I can think of.

-Battery good at 12.4V, starter turns over engine
-Removed spark plugs one at a time, grounded off, all of them arced fine.
-Removed & cleaned the Dist. Cap
-Checked the inertia switch in the trunk
-Fuel pump works & was replaced about 1.5 years ago, has fuel
-Tried using quick start fluid to eliminate the ignition system, but start fluid did NOTHING. Even tried carb/throttle cleaner. Still nothing.
-All fluids good, tune up was done about 6 months ago

Any thoughts or suggestions would be greatly appreciated! Thanks!