Agreed, but they did vary between years and/or models, even though they looked similar.
I tried to use one from a ~74 Dart on my 65 Newport and found the firewall mounting studs were in different places, even though the baseplates looked almost identical. I thought, "easy I'll just put the Newport base-plate on the 74", but found the pedal hole and gasket were a different size so the 74 internals don't fit on the 65 baseplate. I gave up and used the 74 booster as is and drilled 4 new holes in the firewall plate to mount it. I never found a way to buy a new diaphragm to fix my 65 booster, so cut one out of neoprene sheet. It works in a bench test, hooked to car vacuum, but haven't run it.