Larry Wolohon wrote:
"The GN & the CB&Q also had steel reinforced boxcars also that ran to the early '50's I believe."
 
Yes to both.  More on the GN cars here:
http://www.steamerafreightcars.com/gallery/boxauto/gn9731main.html
HO scale kits are available from Funaro in their 3700 series.
 
The CB&Q cars were in Classes XM-17 and XM-18.  HO scale kits are avialable from Westerfield:
https://id18538.securedata.net/westerfieldmodels.com/merchantmanager/index.php?cPath=78



 
 
Ben Hom