Gas Over Diesel!
I have a 1977 Cat 30 with an Atomic 4. Despite warnings that gas engines will blow up, I am much happier with the A4 than a smelly complicated diesel engine. A non-mechanic like me can fix the basics (I even rebuilt the carb using a kit 2 seasons ago). As long as you religiously use the electric bilge blower, you should have no problems. In fact one discussion group message claimed there has never been a documented explosion of an A4 so don't be the first. For parts and reassurance, see the King of the A4, Don Moyer, at www.moyermarine.com. He even answers his own e-mail!