I had a Classic Mk IIC. The C stands for Compact. Its a Mk II but a little bit shorter.
I would advise you to not over power, or overweight the transom. At this age the attaching glue is weakened, and over stressing it will cause it to fail. Treat your boat nicely.
I had a 20 HP 2 stroke Evinrude on mine. That was adequate. I modified the engine to make 25 HP. That was much better. I would say a 25 2 stroke is optimal for that boat. Lucky for you, everyone these days wants 4 strokes and high technology. Get an old 2 stroke. Simple, cheap, light weight, proven, and reliable.
I wish I still had my 25 Evinrude. Pull start (no heavy battery) light weight, and totally reliable.
Feel free to ask me more.