u need an adapter bracket if running the rb motor/trans. (this info is kinda important and shoulda been in the original posting!!!) mazworks makes the trans mount bracket adapter. if its been converted back to sr/ka maybe its still has the the rb trans mount? look at the pics and figure out what u have going on. its ur trans mount bracket in some way/shape/form
RB25 to S-Chassis (S13/S14/S15) Conversion Mounts - Engine - Mazworx