Very cool, Jason. While you're at it, you should basically re-make the entire main chassis out of steel. More weight, more traction.
As for the details, just look at the real WA500 loaders and add what you see. Mirrors, light buckets coming off the frame area where the loader arm pivot bushings are, and nicer hand rails. That rear grille could use some detail too. Don't forget the windshield wiper! Any place to can get rid of the scew heads, definitely consider it. Nothing ruins a scale model like phillips head screws sticking out of a sheet metal body, where there shouldn't be any visible. Weld things together instead. It almost looks like you already made the front half of the chassis out of steel and welded it?