A pet peeve of mine with Williams diesels is the grossly undersized fuel tank on most of them which severely compromises their appearance. Sure, WIlliams models are not touted as 'scale' but a simple improvement here can yield good visual results that greatly enhance the appearance of them. Not liking the 'high-water' look of Williams' models (especially the Alco PAs) I decided to try to do something with a BNSF Dash 8 that I've had for many years. I removed the fuel tank and cut it lengthwise, adding a block of wood to increase the width while adding a sheet of balsa to increase its depth. I then painted it (and the trucks) silver to help give it more visual impact and viola' - it appears much better with a more massive look, like it is hunkered down on the rails.
This particular unit is a testimony to the durability of Williams engines. I bought it when these first came out in 1998 or so and other than oiling occasionally, it has needed nothing to keep running smoothly. This one gets a lot of run time on the club layout. It's been amazing...