200 hpdi on a 18

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I have an 18 I'm just finishing up putting a 150 mercury 2 stroker on. I believe it weighs in at 415 lbs. The boat had a 1987 mercury tower of power inline 6, 115 h.p. on it when I bought it 11 yrs ago. top speed was 39 mph turning a 17 " pitch prop at 5500 rpm. wgt was 316 lbs, and when three men (all over 200) got in the back water would start to come in if the weight was to one side or the other. I figure the 150 would be border line in the weight dept. I have seen 18's with 200 but they were mercurys and all 2 strokers. You can always put plugs in the drain holes. I had a 16 C Hawk with a 70 Yammie on it and needed to plug the drains. It was never a problem, The boat was rated for a 70. I just never took it where it did not belong. I would find a lighter 200 if you want the speed but I would also check around to see if the hull can handle the speed as you should be in the mid 50's or better turning a 21 inch pitch prop. A 150 mercury 2 stroker should put you at or around 50 mph turning a 19 inch prop. You would need to go to double steering cables or hydr. steering. a Single cable would not handle the torque of the 200 at speeds over 50 mph. I don't know of a bracket or jack plate would help. either one might increase the effect of the weight of the motor as it moves the wgt. further back. I doubt if the steering cables could make the bend either so hydr. steering would be needed or you could re route the cables out the transom above the battery. You could run into legal problems if something happened and you did not warn a passenger that the boat was over powered before they went for a ride. Butch