What is the scale of these cars? For my tastes, they look too small to work well with most Standard Gauge trains and accessories. However, they should be perfect for O gauge tinplate.
For SG, I prefer using 1930's era "pressed steel" vehicles in 1/32 to 1/25 scale such as the fire engines by Girard or Marx:
pressed steel buses by Keystone or Kingsbury:
and pressed steel trucks, cars and trailers by Wyandotte:
As for die cast, I prefer 1930's era casting by Arcade:
or their modern era reproductions by Pride Lines:
The size of all these seems to work well with my mostly 1/32 scale SG trains and accessories.
Some day I may be able to afford a modern era die cast truck or car by Tom Sehloff,
Bob Nelson