Well, the hunt for E31 840i brembos just isn't fun any more so I gave up. And then came across these on ebay.
2013 BMW 1 SERIES M135I M SPORT BREMBO 4 & 2 POT FRONT & REAR BRAKE CALIPERS KIT | eBay
The nice chap selling these has even included the mounting pitch of... "APPROXIMATELY: 12CM" for the front and "APPROXIMATELY: 7.5CM" for the rear.
So hear is what I think:
The fronts will fit on to the m3 evo hubs with possible a e46 m4 or more likely a csl disc
The rears not so sure about but hope fully a straight swap onto the rear discs or worst case scenario e46 m3 rear trailing arms.
Obvs the disc PCD would have to be similar...
(Disclaimer: Actually worst case scenario is that I'm talking pure shite and none of it works )
Maybe this has been discussed before... any one heard anything about this!!? (if not, you heard it here first! :P )