No problem with a salvage yard engine, and no immediate problem with using it in a 85. Except the injection pump is different in 85. There are a number of slight differences like a crank sensor that is used for engine speed for the A/C system.
The car would need to be set up as the earlier model.
The major problem here is that you will have better than 3-3500 dollars of value by the time the project is finished and you will still have a used motor of dubious history (I didn't know that salvage yard motors ever had more than a 100k [bg])and minor rigging.
If you are planning on selling the car the whole project is poor. If you are planning on driving the car a proper rebuild has much more value.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician