Ok, I put that all in and so far it's working ok. I'm still making tweaks to get the positioning right. However, I've hit two things:

I watch the two particles, and I can see them doing there thing. However, I cannot apply this to my overlaying shell movieclip. I need to find a way to find the difference between the two particles now, such that it allows me to find the angle.

In other words, it doesn't seem to have solved much of my problem, just recreated it in a new way.