To add to what Dan said..
Once a truck leaves the factory, lord knows what happens to it.
Maybe the truck was a glider kit and the owner added a suspension from a Peterbilt to a Freightliner or rebuilt an old Brockway using a Pete air suspension.
Anything goes!
The suspension that Italeri has in most of the north American kits isn't a Freightliner suspension. The suspension was originally designed by Western Unit Co., called "Staibilaire" and marketed by Peterbilt exclusively until the early 70's when Freightliner obtained the marketing and rights to the suspension.
If you compare the AMT Peterbilt 352 and the original 359 kit, it has the same suspension, just not as nicely molded and detailed as the Italeri version (1/25 vs 1/24 too)
Tim