[Steeveedee]

The "pop" is probably a bad plug wire, given all that has been replaced. I've never seen a plug that gunked up at 4000 miles, unless the valve cover isn't sealed up well.

As for hard starting, does is crank slowly (heat soaked starter, very common) or does it spin a lot before starting (carb boiling over, needing a thermal insulator)?

As far as the gap being closed up, the installer probably dropped it and put it in without checking, or it was dropped in the box before that, and not checked before installation.