I found and just read about RigB which stands for Rigid Body,
RigB Article I found
I often recommend the 540 as a starter MM cartridge, however, I would spend any extra money moving to a MC Cartridge.
I highly recommend my choice.
AT33PTG/II $490 or BO
Any phono stage, try for return privleges, as it is 'preferred not better' that you will finally cross paths with and feel lucky.
Think Long: Options for a variety of future cartridges, Stereo MC; Stereo MM, Mono. SUT with PASS for MM and use existing or future MM phono, keeps options open for using any Vintage Phono Stage.