Nice looking rig! Yellow is very bold for a truck!
I'd trust 1985kenworth for all of the figure and bodywork stuff.
As far as gear reduction, I'll add that I also do not run a GRU. I ran with a 1:4 unit on my KH for a bit, but it was too slow for me. Worse than that was that I found it put a lot of slack in my drivetrain. More gears means more space between teeth, and therefore more room for the truck to slide around. I could roll my truck back and forth about 12 inches more than usual, which is no good for putting power down, or setting it on tables.
That is my 2 cents! Take it for what you will.
-Chris