I don't know of any racks, at least not made by Opto 22, that support multiple brains like I think you mean.
However, I'm hoping you know about the feature in PAC Manager under Tools > Import/Copy I/O Unit. That might be helpful depending on what you're up to there, and what you have configured on those brains already. Why are you replacing your SNAP-PAC-EB1 brains? Perhaps upgrading to SNAP-PAC-R1s?