Mercury specified TCWC3 certified oil, mixed 50:1. I use 40:1 in all of my old green and white Mercs, just as a precaution – oil is cheaper than parts and more available. Have used Tech brand from Walmart for years. Use lower unit oil recommended for shift gear boxes.
Mark 5 coils – is that Bendix or Phelon? Old Outboard Jim may have them.