The older OMC engines (Evinrude/Johnson) do not need extra parts to hook up. You just connect the throttel and gear cables on the outside of the engine. I have some OMC engines from late -50s to early -70s, and they are easy to hook up.
Also have a Merc that needs a big rebuild with unavailable parts to hook up. Merc also change the direction of the throttel-cable push/pull in the -80s, so you have to find the correct controlbox for the engine you have.
Unless you can have the parts for free from a scrapped engine, go with OMC. Or buy a engine complete with cables and controlbox.
I checked the price for rebuild of the Merc I have (25hp), and with used parts from a dealer I was halfway to a used 40Hp Yamaha complete with everything. So I bought the Yamaha