i remember seeing a vin stamped lightly into the frame near the steering gear on my Canadian 58.
I found this interesting, maybe the start of a federal program? sorry, don't mean to go down a rabbit hole, but this may be relevant. a wire brush would be good to take with next time just to see if the frames have a vin so they can be matched up to cabs if possible
https://www.stovebolt.com/ubbthreads...94227&page=all