Mx13 axle plates are 153 mm diameter.
The centre locating ring is 60mm like ae86 diffs etc.
I had a U13 rotor laying around. Its a 257mmx 12mm solid rotor, 4 x 114.3, the inner area where the axle plate sits is also 153mm, it was a tight fit to the mx13 axle plate. this rotor has a 67mm centre bore.
Its almost perfect except it isnt vented.