December 2012 GCR:

Either the OEM transmission or an alternate transmission must be
used; the alternate transmission must be from the same manufacturer
as the vehicle (e.g., an Acura transmission may be installed
in a Honda car). Alternate transmissions must be used in their
entirety. Retrofitting OEM complete gear sets in an alternate transmission
case is permitted.

August 2014 GCR:

Either the original transmission or an alternate transmission must
be used; the alternate transmission must be from the same manufacturer
as the vehicle (i.e., an Acura transmission may be installed
in a Honda car). Alternate transmissions must be used in their
entirety; any OEM gear sets that fit w/o any modifications to gears,
shafts, and/or case are permitted.

The change came as a request from the CRB.

I think the verbiage change clearly implies gear pairs can be mixed and matched. We'll see what the STAC/CRB says.

GA