If you really want to add some engine detail you might be able to add fuel lines, and possibly airlines depending on the kit they may or may not be molded in. The engine in that kit is a Detroit Diesel 8V71, I'm sure a search on ebay will find a few trucks for sale with that engine and may include some photos.
I have a few pics of motors including a DD 8V71 here
http://www.geocities.com/cnf_e32/details/motordetail.htm
You can get actual Detroit Diesel Alpine Green from Duplicolor, I've also found WW2 British Interior Green is a close match. Detroit Diesels are notoriously greasy, oily and in general filthy so if you get the color close you can weather it like crazy to cover up any slight variations in color.