Go online to: MarineEngine.com. They have everything you'll need to keep that old Johnson running. I have ressurrected a 1961 5.5 Twin with parts from them. Good prices, quick shipping. Their parts breakdown pics are invaluable in your rebuilds. You'll need a model number off the plate on the transom clamp. If you're smart, you'll order a new water pump impeller and lower unit seals at the same time. Don't ask me how I know that.
Good luck, IslandJim
I'm an Eighth Day Adventist. On the Eighth Day, God went fishing!