r30 and hr31 have same geometry so no different, if u try'd fitting hr31 arms to c210 crossmember itd be wack.
i also run the hr31 swaybars didnt even try the original r30 rear.
if your needing any hr31 rear end parts letme know ive got a few complete rear ends there 4.3 clutchpack, 4 bolt cv's etc
jon.