Hi Luke,
I second what Alan has said re: poss bent valve or incorrect timing (I think the slight misfire is the clue?) but a comp test may not show this very clearly. A cylinder leakage test may give a better result. Whatever it is I am convinced it is linked to the original problem.
If you have a misfire you will almost certainly have a suspect waveform on the ign but if you post the waveform and more details I'm sure someone with better knowledge may be able to pass comment/guide you on that.
HTH's,
Bryan.