The shift mechanicals for Merc were the same from the 70s to the 90s, and likely beyond. The wiring was pretty much the same for most Mercs from the 70s to the 90s. The motor plugs changed, a couple of times. If you want plug and play, you will need to find a control and harness that is compatible with your year motor. You could graft the old motor end onto the new control wire harness, if you cannot find one that matches.
Controls are pretty hardy. I still use the one from my '77 Merc. It works fine. I did need to put new wires into the control box as the originals were rotting away. Maybe you can repair your existing control. Some parts are available.
