I wasn't originally going to post about this, but the weight difference ended up being bigger than I expected. I noticed a while back that the CSL has a different aux coolant pump than the M3. This was probably to allow it to have more clearance to the airbox, but maybe not (since the stock on cleared). The CSL used the same one as the non M e46 (64118369805), so when I randomly stumbled upon one I grabbed it.
Dry weight between them is 1.22 lbs per realoem, but I suspect the actual weight difference is a little more since it fills with coolant.
CSL/e46 version:
http://www.realoem.com/bmw/enUS/part...&q=64118369805
M3 version:
http://www.realoem.com/bmw/enUS/part...&q=64118369807
Wiring was pretty easy-- the M3 version has two plugs, whereas the non M version has 1. One of the plugs from the M3 part connects to the non M version, so I used that, cut off the other and taped it into the harness, and all seems to work as expected.
Size comparison:
Installed:
I fully understand that 1.5 lbs isn't much in isolation. Just working on pushing that weight distro back to 50:50.