As you have done the plugs leads then check your electrical connectors to the injectors and any off the wires running off them if they run into the push/clip together black connectors ford use (I can't remember proper term for them) then they can cause problems.

Over the years the pins can corrode and you get poor electrical contact so they start arcing inside making it worse. Everything can seem fine but it only takes you knock them while your doing another job and if the connection is only just making contact then you can make it worse.

I good idea is when the engine is running, is to go around and give all the electical connectors a good tug and a twist if you've got a lose one it should be pretty obvious .

As others have said it could be done to a millions things but with cars this age it is normally down to elctrical connectors / wiring. Old wiring is bad enough old ford wiring even worse .