Gah! The bottom of the port is not the crucial point. It's the top. However they are of course on the same barrel so raising one raises the other and the transfers. Rule of thumb is higher exhaust will be more top end with trade off at bottom. I've only played with gaskets on 200 and 300, so cant give experience.
As far as the head mods go, it depends how much you trust the person who did it and how close in tolerance your bike it to theirs plus what gas you will run. Read my thread on 300 head mod. Principle is the same and will clue you up what simple measurements will keep you safe and get most of the advantages on offer.
It's a bit rambly but gets there.
http://www.gasgasrider.org/forum/sho...highlight=Head