I bought the car back in December of 2011 and it had a plenum spacer and JWT PC installed. One day me and a friend were looking at each others Zs. Comparing his plenum to mine, mine looks "newer" on the lower half than his but are both 2003. Is there a way to tell without taking the plenum apart if you have Mrev2 installed or not?

 

I'm assuming you're talking about the upper most portion that you can visually see under the hood? That has nothing to do with the MREV2. Also, no there isn't a way to tell unless you take the plenum apart and look at the runners. The front two will have 5mm of material shaved off of the top.