Coilpack still uses the phase sensor, as you have just got the car I would do a mega service on it, not forgetting the fuel filter, and also a fuel pump and fan rewire if you want it to last, at this power it should have a 044 pump, if on std it could have problems, especially if the 20 odd years old one.
They suffer terribly from volt drop under load, and so run lean, the fan circuit is crap and most burn out, so a rewire is on the cards just for security.
As to the misfire, is it only under load ie if in say 3rd gear just letting it rev out over 4K is it ok ?
Plugs are a fave, as is the phase sensor wiring on the sensor itself, it breaks up and falls off, leading to shorting, but don't think for a minute it's this, something to look at though.
What plugs are you using, what CO is it running ?, what's the spec ecu chip ?
tabetha