I have to agree Fractal. My Gustav's need like 10-12 mm between the rotor and the wheel (in my case, the chainring for the left side electric drive... see my A-Line build thread
Sadly the Gustav's have been out of production about a year. You can still find new pads for them, and find used Gustav's at pinkbike and ebay. I bought 2 sets back in April, took awhile & lots of effort to buy.
If you do go with the Gustavs, note that they originally shipped with a bunch of mounting adapters. You can still find the pdf showing all the options if you search. These things went for $50 and above originally, and are much harder to find than the brakes only.
If you're buying a front brake only, expect to pay about $150 for tthe brake/line/lever and mount, un used but very good condition. If you're lucky the brake you find for sale has the mount you need. If not I'd walk away, nobody wants to break a set by selling only the mount.
Great brake, lots of stopping power and uniquely meets the need of a narrow inside profile. It's a shame Magura stopped making them.
1st build: Dahon Jetstream folding bike
. Quick, reliable, capable of 30mph. Light enough to lift, folds for easy transport by car/bus/train.2nd build: RC powered 2009 Norco A-Line
. Top speed 31mph. Built like a tank, it's resistant to Boston potholes, can stop on a dime, easily goes up/down curbs when necessary.3rd build (just started): Scratch build
ultimate utility bike.