Gas Vs. Deisel (are we crazy?)
I too have an Atomic Four, an early model in a Pearson Triton and have to give it a thumbs up. It was designed for marine use with very low compression ratios thus you don''t get the noise or vibration you get with a diesal.
The real beauty is any "shade tree" mechanic, myself included, can fix it. They are very simple engines and few things can go wrong with it that you can not fix with some basic knowledge and basic tools. There are over 40,000 of them still in use... I think that speaks for itself. I have left the points and condensor on mine since my thoughts are K.I.S.S.... generally if it is not firing it is simply a matter of using a piece of paper sack or a match book on the point and you are good to go again. (However, I do carry spares, as well as, Don Moyers bible-- just in case--- but the engine really is amazingly simple). I also have an old British Seagull on my dink, another oldie but goodie.
Most importantly, buy the boat you can afford and go now. There are numerous older boats in your price range and often you can find an old boat that simply needs to love to become a safe reliable home. Just today in the Annapolis paper was a free Catalina 27... they are out there, just keep looking and keep learning and planning. Fair winds. Ang