[PANAVIA]

Have you checked compression ?

The heads could be anything / the 4F5 is a casting date which means ( if they have the large plugs ; "7/8 socket ) the heads were cast may 4th 1975 , as the small plugs came into production in 1977'

The ford part number on the Windsor ( and other 289-302 ) heads is under the intake surface on the deck side of the head, this is very difficult to read when the engine is assembled.

As for plug selection there are options , but it would be good to know where you are on timing and ignition

Steve