Ive done it, but I have not done a write up on it. Its not difficult though really. There are literally hundreds of pics floating around in which you can use as a guide. The intake side I think is the hardest because the way it is made. I ended up buying a die grinder with a 3" extension on it so I could get way up in there. But I basically just smoothed it out (there was a lip on the intake where the TB mounts) and took out the lip so there would be little obstruction to the air flow.
I plan also taking out the divot as well, I'll just use some quick steel for that and smooth it out but Im also doing some other work further up in the intake as well thats kinda hard to describe.
On the outlet side Im going to close up the side slits on it and actual outlet you basically are just enlarging though maintaining the overall shape is a goal here. I'll see if I can dig up some pics that may help out, but if you search or google for ported M90 pics you should come up with plenty to give you an idea.
