Yamaha 40x engine

Hi Guys,
I have a YAMAHA 40X on my Thundercat Inflatable Boat, is a 2 Cyl, 701 cc two stroke engine (Known in Australia as CV40)
Anyone have experience with this engine?
I know that in not enough power to my boat, but in my country is not available the 50HP 2Stroke.
I like to modify it to obtain more power and speed.
I will shave the cylinder head to increase compreasure, but I don´t know how much ¿1 mm is ok?
Also I like to porting, but I don´t know if open ports only wide or also up, and how much milimeters.
The exhaust tunner will be modified but I don´t know haw.
This engine have only one carburetor, I like to jetting. Actual size is #170. How much I can reduce without burn the engine?
The reeds also is a problem, Boyesen don´t have reeds for this model, and are diferent design, like a flower. How much can I open the stopper? Actually is 10 mm.
The gear reduction also is a problem (2.00 26/13) Anyone knows if the 50H gears can be installed without a mayor modification?
The gas quality here is NOT A PROBLEM, (one good) Premium Gas is 100 RON, and I can use a good quality Syntetic oil also.

Any help and guidance will be greatly appreciated.

FOGO