PartsBase.org lists them L+R, as the same part number, meaning they can be used side to side.
51054L MB618218 SUPPORT, FR BRAKE CALIPER, LH. Period: 1990.06.1-1992.05.3; 01
51054R MB618218 SUPPORT, FR BRAKE CALIPER, LH. Period: 1990.06.1-1992.05.3; 01
So, they appear to be 100% interchangeable. Also used on the following vehicles:
3000GT (MMNA) [Z10#] 1990-1999
3000GT (PUERTO RICO&GUAM) [Z11,16A] 1990-1999
DIAMANTE (MMNA / MMAL) [F16A] 1991-1996
DIAMANTE (P.RICO&GUAM / MMAL) [F16A] 1991-1996
DIAMANTE WAGON (MMNA / MMAL) [F07W] 1992-1994
ECLIPSE (MMNA / MMNA) [D20#] 1988-1994
ECLIPSE (MMNA / MMNA) [D30#] 1994-1999
GALANT (MMNA) [E30#] 1988-1993
Just be sure to confirm the slider pins are identical and that they move freely when inserted and with pads in place/bolted up the the calipers. As long as there is not drag and you can wiggle the caliper in/out some, you should be fine at that point.