Thanks for posting this.
I checked out Tim's website much more and he made several variations of the 579 (daycab, sleeper, etc) some on a modified Italeri 377 chassis.
It looks like he mainly focused on smoothing some lines, replacing the mirrors, opening the grille and using oval screen, and moving the front axle a bit forward and down (for the ones that he kept on the original chassis). Of course, he removed and filled the buttons on top and primed and painted. There was a couple of minor corrections to the fenders, and bottom of the cab lining up with the bottom of the sleeper, amongst other things. Not a turn-key project, but nothing too bad.
I'm guessing the overall proportions are good. Maybe not 100% accurate, but very close. He seemed pleased, and I consider him the expert. I tried to gather as much info as I could from the text he put with the workbench photos.
He also made some mods on the lowboy and that looks really good.
I'm now thinking this will be a doable future project, I just need to get my hands on one.