1986 5.0 In storage 6 years. OVerheats above 200 degrees within 10 miles. New waterpump, new oversize radiator, new clutch fan, new thermostat. New spark plugs. Tested all plug wires.
Slowly continues to climb up temperature.
The 5.0L does seem extremely hard to "burp" I had the same issue as you and it was always trapped air in the system. Pull whatever plugs you can and try to get that air out.
Jack up the front end as high as you can and squeeze the lower hose several times, start it up and let it idle a few minutes while squeezing the lower hose a few times. They make a funnel just for filling cooling systems
Assuming this is EFI, 200 in 10 miles isn't overheating, normal running temp is anywhere from 200-215 on these engines. A stock 192 thermostat doesn't open fully until 212. How high has it gotten while still climbing?