At 9.8:1 I'm not sure how much boost I would want to throw at it. And you get up over 700 hp, xr or not a bravo will not be your friend . You have 2 motors, leave one in the boat and enjoy it while you do a proper build on the other

What exhaust are you running?

stainless marine 4 '' nickerson said that would be fine and spoke to me about past experiences that have worked fine i understand it takes alot of hp to move this 271 but in life a mans word is his word and thats all u got sometimes i was completely mislead and am excepting this regarding my dealings w this builder

Have you considered what running a thick head gasket will do to the quench?

please dont take this the wrong way...I want your build to be succesful and your goals reached,,, just trying to save you more headaches.... Im not an engine builder by a long shot, just finished my first motor, but as I found doing that its not as simple as just bolting parts together you think will work. I dont know what you want for quench, but to much can actually lead to detonation even with lower compression if you have too much.... those non blower piston and rings which had enough gap NA can butt ends and shatter the top pf the pistons under boost.... Your going to need some major carb work to go with the procharger and probably need larger diameter from the tank back and it just keeps going........

THats why I suggest keeping the other motor, building one over time while enjoying the boat with the other motor, while you use the right pistons, rings, the right cam etc.... Plus that gives you a backup motor should your new blower motor go boom. It keeps you from getting discouraged as you keep spending money on more parts while your 27 foot yard ornament collects dust and your friends are out on their boats.