you can use several different parts off the EC such as the shocks and shock towers but there are some things that wont fit, like the radio tray. You'd have to change to the EC chassis in order to use it. There is a good cross reference on the website that shows what can and can't be used. You can find it under the downloads for the XB8R on teamxray.com.
I've got 2 XB8R's as well that I've been running for awhile. I've got a set of EC shocks and towers to put on mine but haven't found time to do it yet. I've got the 4mm alloy front upper plate, 4mm steering plate, alloy braces (that I don't use much), CNC engine mounts, and the alloy suspension/arm holders. The suspenion holders were probably the most useful thing I've gotten. A full set of those was worth the investment.
My son's has the heavier 4mm XB8R shock towers along with the CNC'd engine mounts and the alloy center diff top plate. I meant to put that diff top plate on mine but my son got to see it before I mounted it and he had to have it....
One of these days I might get around to buying another one but the stock one works fine. I just like the look of the alloy and I suppose it makes brake adjustment a little easier.
Take care,
Matt