Yes, the general reason for a COE was to have a short tractor so you could haul the largest trailer allowed within the length laws of the day. Length restrictions were very strict on the East Coast, while not so much out West. Should the Transtar 4070A kit have a shorter wheelbase? Probably for East Coast work. Remember a longer wheelbase gives you a better ride.
I do not know the history of this particular kit, so there might have been a reason for the long wheelbase when the kit was originally designed.