You'll need to use at least 10-12 mm spacers (probably thicker on the R) to run a square 9.5et35 wheel setup on an e9x M3. FYI, this is the wheel width/offset BimmerWorld used on their GS class e92 M3 racecars (now competing in club racing, 25 hrs of Thubderhill, etc. with one of them; yes, they used spacers to run these wheels on their racecars).
With your SC a 265/35 tire sounds like it's a bit narrow for the R so I'm not sure a 265 square setup is ideal for you. I don't have a SC and I'm running a 265/285 tire setup on 9.5" F and 10" R wheel widths - with a SC I'd run this or a 265/295 setup (or even a 305 on the R with a 11" et33 wheel).
A 9.5" wide R wheel limits the max tire width you can run - 275, maybe 285 for some tire manufacturers.
These wheels should clear your Brembo BBK. Are you running their 380/380 6/4-piston BBK?