[Bushwacker]

You're right to keep an eye on engine weight, because balance really affects performance and ride, not to mention self-bailing capability. Most of the new 4 cyl 4 strokes are almost 500 lbs if you look at wet weight and include the cowling, and that's too heavy for the 20' hull IMHO. Heavier engines will increase min planing speed, and the cc models seem to be more stern heavy than the Seafari, so I'd try to mount the console and batteries as far forward as possible. My Seafari would easily plane at 12-13 mph with a 300 lb V-4 and the boat rode very well in rough seas. Current setup will do the same, but it took a stern-lifting 4B prop to get there. The 140 Zuke and 150 (actually 165) E-Tec both weigh about 429 lbs and are about the heaviest I'd consider. Unless you want twins, I'd go with the small V-6 Merc for min weight and decent mpg. Check Big Shrimpin's posts for his results with that rig. He's one of the resident wizards on setting up those motors! Good luck with your custom rig! Denny