you don't need the GCC. in fact, that is overkill and may actual cause some issues having so many things modify the airflow signal.
also, be sure you hook up the afc AFTER the vpc, despite what hks says. i.e. the output of the vpc to the input of the afc. it works much better that way. you may also need to add a resistor on the intake air temp sensor to avoid the ecu setting a code. you may know about that already.
if it helps, i think i have some drawings of how to hook it all up if you have an 89+