I just used a rotozip saw to do the rough cuts, and then used a large metal file like the ones used to sharpen lawn mower blades to smooth out the cuts. buy plenty of rotozip bits though, they will break after a little useage. much faster this way.
i grinded the inlet on all sides of the case and inlet plenum outlet as far as possible, leaving about 1/8th inch contact all the way around.
then grinded the outlet vee a little more than 1/4th inch all the way around- grind down those screw recesses too.
last, i grinded some of the inlet geometry extending the vee shape towards the front inside the casing. within the vee shape there's a notch point on the bottom inside the case- i grinded that down a little to extend the sweep area of the rotors to help it pick up a little more air and reduce rotor chattering noises.
with all of that done, on a stock pulley i can get 15 psi at 4500 rpms. with a 5% pulley you'll get close to 17 psi on a stock exhaust, but this of course is not good. heat becomes a factor with flow issues if you have a stock IC and then you will have detonation. hopefully you have upgraded your exhaust and not run into this like me.
i am very pleased with the increased power though.