I ran a GT30 4" intake that fed back to a Z32 AFM size... 24psi/370rwk was no issue on fuel, 270rwkw on 17psi on PULP.
As long as there is a reasonable amount of 4" piping to a reducer to the AFM size, it'll be fine.
There was a thread about this recently actually, ended up 2-3 pages long with examples of a 3" to 4" pipe, lots of setups 300rwkw without a problem.