There is 4 screws that hold the head on... On a scale of 1 - 5, 5 being hard, this is no more than a 2...
Look at the glow plug
At 4 corners of the head you will see holes with a 2.0mm hex screw in it.
-- You might be able to see them through the fins...
Loosen each one until they have come out of the block.
Pick up the head up slowly
All the screw should be dangling...
The button (under head) will still be in the block.
Grab the glow plug and gently remove the button from the block.
The head shims will be located in the bottom side of the under head button.
Look at it from the side and you will probably see them... I believe the silver one hides the copper one. Be careful though they bend easily, so take your time.
I can't remember exactly why, but these engine are pretty much shimmed for 30% nitro. Supertib knows the exacts, so if I can find the post that explains I will post. Removing the silver shim will allow for lower nitro content fuels. That is the best I can offer right now.
Yes I did fill the front windshield full of holes with my reamer
The gas tank thing was a big myth with the Savage community in regards to the 1/2 tank lean problem... It is true if it is not seated properly then an air leak will form, but if you lid is not seated properly then the spring is no good and that means parts replacement.
Hope this helps... If you have any questions, comments or concerns you know how to get a hold of me...