This might help:
FOREWARNING: If you are poking around inside of a CRT TV/monitor & don't know what you're doing, it can be very dangerous for you if you're allergic to high powered shocks! The kind that could possibly maim(not the emu) or kill you!! So don't do it unless you have at least a general idea of what not to touch, even when it's unplugged...The flyback & caps can(& should) hold a high charge for quite a long time...possibly days...so take care when attempting a repair or adjustment. Or not, I've seen people on U-BOOB who surprisingly hold little regard for their own mortality...
If there is no digital menu(I think this TV is from around 2003 so there probably isn't) to change screen size you'll have to look on the TV's chassis PCB for some potentiometers(or they could be on a daughterboard or the neckboard). These should control all the aspects of the picture that the tube emits. Adjust them accordingly so the screen fits again or to your liking, whichever. I'm assuming someone already cracked the CRT out of the main box already to mount it in the cab, so it shouldn't be too hard to find what you're looking for, if not, you're going to have to open up it's case first.
Sorry if this wasn't helpful, maybe someone else is more familiar with this model or has a better idea of how to do it.
Pessimist: Oh, this can't get any worse!
Optimist: Yes, it can!