This is a really simple answer, you don't need links or Cisco white papers, and it is all based upon the physical design of the PCB edge connector of the supervisor engine. Anything beyond a supervisor engine I will NOT even fit into the 4003 switch. The multipin PCB connector (white) on the SUP I is thinner (less pins) than the multipin PCB connector on Sup II thru IV. You would need a billy club to make a Sup II or above fit into a 4003 switch.