Yes, I did have minor interference issues on my App, but as I don't use the FORD MOTORCRAFT CAP you are referring to anymore I don't remember what I did to get around it!
Seems like one of the spring hold down clips touched the manifold at certain advance settings so I had to lift the dist and reset it, was all.
BTW I just use a stock cap now and don't have any arcing problems as yet, We'll see with the new HP and on day to day use.
A L A N F R A K E S ~ Tulsa, OK