How difficult to file fit rings ?

Not to hard at all Just sink in the block in the respective cilinder and square up with a piston and then mike with a feeler gauge to see what needs taken off for manufactures end gap. This should really be done to any performance engine as if it ever runs hot or you spray no2 and they butt it really does damage to the cylinder walls and may break and blow a cylinder. Time well spent in my opinion .The difference between a rebuild and a custom built motor. Jegs sells a hand crank ring filer at a reasonable price or a smooth blade en a disc grinder will also work,and dont forget to bevel when done.