The Rotrex is certainly easy to mount but there is room for a Vortech unit or similar brand. With the factory air box gone there's a ton of free space opened up. You could also relocate the washer fluid tank if you needed even more space.

The Eaton units can be installed (there are a couple of guys on the forum with them on M103/M104 engines) but the mounting hardware will require some skilled metal-fab work.

I've added a few more shots of the system to the folder including the blowoff valve and gauges if you are interested:
http://www.imagestation.com/album/pictures.html?id=2099787672&code=25139088&mode=invite&DCMP=isc-email-AlbumInvite

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2002 E55 Stock
Sold my project car: 1993 300E (3.2L) Blower running 0.8 Bar, Re-badged E32 Kompressor, Apexi Piggyback ECU, 310cc injectors, 255LPH Walbro Fuel Pump, Water/methanol injection, Quad SS Exhaust Tips, 3" SS exhaust with high-flow Cat, 17" Monoblocks 225/45/17, Brembo BIG Brake upgrade, Euro-headlamps, clear corners, Euro-tail lamps, keyless entry, CD AMPs Subs etc...

Photos: http://share.shutterfly.com/share/received/welcome.sfly?fid=c20c2dad4373aa89&sid=0CbuXLVo5cMXFg