Cutting up a Globe Liner

[Espeefan]

Hi guys, I'm not that great with body work, but I am working on a Globe Liner cab, for practice. I'm hoping to make it look more like a Kenworth K100. I want to cut the wheel well opening, so it starts closer to the front of the cab, but I really don't know how far forward I can push it. The whole bottom portion, aft of the wheel opening needs to be shaved off, but how much do I cut to the front? Any guide lines, or advice? I do plan to slide the front axle forward too. Thanks!