Don't get all butt-hurt. Without putting it into writing early on nobody here knows your mechanical expertise.
If you are not great around boat motors the best you will do is find a 15hp carb, change it out, and claim you turned the engine into a 15hp.
Your research into the other parts may be pointless since you have to remove the powerhead to change from an exhaust tube to a tuner. You have to remove the intake manifold then the reed blocks to install the additional spacer, if needed. That is where your research would come into play. some of the later years had these changes already just for commonality on the assembly lines. Am happy to tell you what needs to be done but I will not do all of your research into part numbers as well.
Not being mechanically inclined you may this may be a bit much.