I converted all 4 corners of my 914 (911 struts up front, 5-bolt all around) to Porsche Turbo calipers from an 87 944 Turbo (same as a 911 Turbo but smaller Brembo casting). Discs are 11" vented Carrera parts, and they fit under 15" rims. Simply stunning braking, and not as obscenely expensive as you may think, since the calipers are readily found in wrecking yards (C4, 951, 968). I've converted a number of other people's 914s since, and finally made the fixtures to do it faster/cheaper on a CNC mill.
I've also done the same setup up front with the monobloc Boxster caliper, but those are harder to find used ($275/ea new). I'll be adapter the rears soon. All bolt-on, since I'm bad at welding!
Anyone interested, shoot me an e-mail at [email protected].