Assuming you know how to install the nitrous, I would recommend you start stocking pistons, rings, engine blocks and rods. Nitrous is a great bolt on tool to make alot of power with the push of a button, but, the engine has to be completely remade to handle the extra HP the nitrous makes. Ever watch the movie Madison? As cheesy as they made the pushing of that nitrous button, there is alot of truth to what they over dramatized when they blew off the sponson. Having been at that race with my dad in 1971, I was dissapointed in how they made the movie, but it was still fun to see all those vintage boats.

Mark 75 said what I would have. Until you do something below the water line (gearbox) you are not going to see a great gain from the powerhead. Something else. Unltil you do a great deal of work up top, that motor is never going to swing an 18" wheel and get any kind of respectable RPM. We had a 25 on a 10' GW Invader years ago and Michigan Wheel recommended a 17 as a box stock package. We could not ever see beyond 4800 RPM when Red line was 5500. It was so doggy out of the hole it took nearly an 1/8 mile to plane off and lugged very badly on the turns. There is a hole thread here on
OMC 25 HP that you would benefit reading from. Check it out.