Omc 56 tuner questions

[filthy phill]

This might sound a daft question , but what is the hole at the top of the tuner for in the 56 ci OMC 20 inch motors.
and 3 small holes about 1/th inch in the top of the plate ???
pic below shows what I mean about large hole.

I got my spare mid section completely apart yesterday doing some measurements and notices the large hole in the top at the side.
also took notice of the lots of holes at the top of the can itself.
Plus something I did not know and never noticed before was the small hole in the water pipe about 8 inches up from the water pump ?

I noticed that if the tuner was cut about 3 to 3 inches ( from top of adaptor to exhaust outlet end is 11 1/2 inches) it could be made about an inch wider all
round and STILL fit in the can easy enough , so can be made wider at the bottom.
(Not sure if I want to cut the one on my engine I use at the moment )

I also managed to break every single bolt after the very first one came out fine, its like the stainless turns to rubber in aluminium after a while.