The cataysts on SLs to 76 were part of the manifild assy. They wound up depositing the exhaust the same place stock 73-74 or 77-79 manifolds placed it. So a 76 exhaust from the cat back will hook to your manifolds. (and have no cats in it)
The cats in 77-79 were under the car is two pods before the exhaust went to the center of the car.
Bosch Master, ASE Master, L1
33 years MB technician