We had this debate at work many times to inconclusive ending.
we called the dmv , Secretary of state office and the state police.
I dont think the state knows its own law
The dmv will for sure want to sell you a "D" plate. Now that said as long as your truck does not weigh over 8000 lbs. at any time you should be fine. Im kinda in the same boat here with my 2500HD.
If you are over 8000 lbs no other plate can be on the truck but a D plate or higher.
No blackhawks, cubs, bears, bulls, white suxs or B and so on.
Ill. does have portable scales and they been know to use them at times.
From my understanding playing dumb after the fact dont work. The fines are lofty.
Il. is a money hungry broke state.