Right now due to funds only front-end is being tackled. Prep, paint and installation will be more than the parts themselves!
After recently getting the BMW Performance (V2) Power Kit installed and this work being done, my credit card is hating me right now (although the credit card company is loving me right now)!
Honestly, with the APEX ARC-8 wheels I have, I can already fit a 275/35/18 in the rear and with Bridgestone Run-flats under extreme suspension travel or high-g turns (slight tire deflection) I notice a little wear spot in the passenger side rear "cloth" inner wheel well lining, so I went with 265/35/18 tires. But all that to say, currently I do not have a traction issue with the rear of my 135, just in the front and it understeers like a pig even with E92 M3 lower control arms and Vorschlag camber plates and running -2.5 camber I can go through front tires in a day. After doing as much homework as I could and using those wheel offset calculators online, I determine that an APEX ARC-8 rear wheel for a Z4M Coupe would be perfect offset for my setup and allow me to run 265/35/18 square tire setup (in theory, hopefully to be proven correct next week).
So I may just leave it as-is with only doing a 1M front-end conversion or if the lines of the car don't quite look right then I will consider rear 1M-like fender flares. Of course I like the styling of the rear bumper of the 1M, but not enough to spend that kind of money when you consider that all the money I spent on my BMW Performance Exhaust would be waisted plus the cost to prep, paint and install -- PLUS then having to buy dual exit exhaust.
I've read in other threads here the same thing; that the 1M rear fenders are not swappable or at least it is left to those with deeper pockets than mine. A another 1M conversion related thread here mentioned that there is a company in the UK I believe that provides a 1M rear kit (1M rear bumper and other bits) and I believe their own fender flares that a shop would have to cut your fenders and weld these in. If they sold just the rear fender flares without the 1M bumper and bits then I might consider that for next year, but that kind of work is time consuming and costly I would think.
Next year I want an LSD and engine mods (CAI, oil cooler, tune maybe). Maybe next winter's project will be cutting and welding on 1M-like rear fender flares?...