Well after sleeping on it, yes I remember exactly what the carbon center is like in the MSD cap, it basically just "plugs in".

Chapper, this cap was relieved a looong time ago and yes it was in place but can't say exactly how long it's been missing.

Bonefish, I drove it around the neighborhood and in the garage at the least like this
That's the last time the cap was off and I didn't find it on the trailer floor either