Just a little add in on trucks.... The R190's by International Harvester Corp. were introduced in 1956 I believe and were unchanged for a number of model years. Lots of them lasted into the '70s and '80s and in my neighborhood there is still one dump truck running around hauling potatos in the summer and plowing snow in the winter. The era for the White 3000 is the same.
As for trailer lengths, I drove trucks over the road until 1984 and by then even 53' was common, if not preferred by shippers of lightweight goods. (I hauled lots of empty aluminum cans, a whole 53 foot trailer load was only 5000 pounds, including the pallets and other dunnage! Was like hauling around empties all the time.)
Anyhow, back to the trucks... The wooden wheeled, chain drive Mack are from the teens and early twenties. By the thirties they had matured significantly, and if memory serves me right, they offered quite a modern vehicle in 1933.
The new models that Athearn is introducing, the B and R model Macks both originated in the mid to late '50s and a few of them are still around today.
If you are into resin kits, check out Sylvan Scale Models for some variety on your road.
http://www.1-87vehicles.org/directory/sylvan_scale_models.php
Also the IMEX vehicles include 1948 Internationals, Peterbilts and 1952? Fords.
When it comes to trucks, their use and length of service life varies as much as railroad locomotives. Some companies traded to newer models regularly while others were rebuilt until there was nothing left to rebuild.
Go to the Walther's site and look up vehicles in the advanced search and enter trucks in keyword and you will be astounded at the number available.
http://www.walthers.com
Just another hint. Unlike cars, it is not uncommon to see 20 year old+ trucks still working every day. So that should help you with matching your era.
Good luck and happy trucking!