There is still guidance from the FAA in the FSIMS for issuing multi-engine ratings with the limitation "Limited to center line thrust." If you take the checkride in a Cessna 336 or 337, you get the restriction. In addition, if you convert military competency into a FAA certificate, there is a list of a dozen aircraft with no published Vmc and therefore the FAA will issue the certificate with the center line thrust limitation.
I've never heard of a 727 rating with the center line thrust limitation. And I don't understand what you mean by saying it's "grandfathered" for pilots who took their ride in a 337. If you take the ride in 336 or 337 and get the limitation and then take another ME checkride in a "normal" twin, the restriction goes away. The FAA lists the tasks you have to do to remove the restriction, you don't have to do a full checkride.