Personally, I sincerely doubt they cruised a single 50 at "it cruises at 12-14 mph". I run twin 40's, same engines for the last 16 years, and I have tried to run on a single. When the boat was light, and with careful trimming and ballast adjustment it would get up on plane, but that is working that OB very hard. It will come up on plane at about 9-10 knots and I don't think I ever got 12 knots water speed out of it. If I had to do a "get home" on a single it would be on slow cruise and with the tidal current if possible. The single will easy do 5 knots (hull speed for the 22) all day long, planing, not so much. Five knots, that is my favorite cruising speed.
Here is the difference between using a twin which is propped for the two motors, and a single outboard which has the proper propeller for planing the boat. The single outboard will have a lower pitched prop, probably with a little more surface area. This is why it can relatively efficiently spin up to rated wide open throttle and then achieve planing speeds.
If you are gong to regularly try and run a boat with twin outboards, on a single motor, then you want to have a set of props of the appropriate pitch for that use. You will have to change the prop when running on the single...not always easy to do at sea.