The Manufactures are allowed +-10% so those 200 hp pushing 220 and those 225 Ho's at 247.5  are still legal.

I hope to soon have a 250 pushing a LEGAL 275Hp.  Your 115 may  be in the 105 to 125 range. If its a older motor the  HP may have been at the crank and then you really only have 95 in todays terms. If you are ever caught in a tournament or worse in a accident  you will be sorry.  You might be able to have the motor detuned or the Coast Guard approve the combinatation.

Motor weight has nothing to do with the horse power unless you are going to a physically larger motor.

In most modern V-6 motors, they only use a few powerheads for the whole spectrum.

In the 3.0 Johnson for instance, the 200hp, 225 hp, 225HO and 250 hp are basically the same motor. They just used a smaller carburator on the 200's than the 225's (even some 200's came with 225 carbs, making the 225's with 200 decals). They opend the 225's exhaust port and changed it's timing to make the 250 and they just changed the decals and lower unit on the 250 to make the 225HO.

Mercury does basically the same thing with the 2.5s.

Evinrude 3.3 DFI's they just change the computer programming and use different lower units.

You can take any 200hp 2.5 Merc or 200hp, 3.0 OMC fishing motor and get 300+ hp from them and not change the weight, other than make them lighter if you want. Just take the know how and a little money. If you don't have the know how, it just takes a whole lot of money.

If you want, you can even adapt a 3.3 block that has be modified to put out well over 400hp (closer to 500 hp) to fit on top of a 200 midsection, all the numbers will say it's a 200 and it will still weigh the same as a 200.

Trust me, this kind of stuff is done all the time. The guys fishing B.A.S.S. Elite's and those level tournaments can't afford to take the chance on running modified motors, but at lower level stuff, bunches do it.