Gain Suite: Win/Mac session portability

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I'm sharing a Reaper session back and forth between my 64-bit Windows installation and a collaborator's 64-bit OSX installation.

The gain suite plugin reports the name "VST3: Blue Cat's Gain 3 (Stereo) (Blue Cat Audio)" exactly the same in both Reaper installations, but neither installation recognizes/loads an instance of the plugin placed by the other person. That's killing the portability of this Reaper session.

This plugin has 2 mac versions of the VST build and 4 versions for windows. For our purposes we can deal with bridging 32bit versions, using VST2 or VST3, etc. Is there some combo of what he and I should install that will let us have portability?

Thanks!