I thought the White Mustang was the engine, not the truck; but what do I know.
Here is one that was owned by P&C Foods here in Syracuse, NY, before they went bankrupt. I have no idea what happened to the truck & trailer.
For the age of the truck, I would go with International Red (Testors Red is a good match) for your Cummins V903. I believe from the factory the V903 & V903T were gray.
There was a good shop down near Government Center in Boston, but I think that's long gone. The best shop that I know of in Massachusetts is The Spare Time Shop in Marlborough, MA.
http://www.sparetimeshop.com/
I'm pretty sure I've seen "In Tandem" on YouTube, but that was several years ago so it's probably been blocked in the US by CBS, or Paramount, or whoever has the rights.
I've always thought that 1/20 was an odd scale when so much automotive is in either 1/24 or 1/25. I guess this will look ok next to the 1/20 F1 cars or sci-fi kits.