5-port spec is a stupid rule. Yes, it prevents the buy of very expensive 9 port engines but any 5 port engine can be modded to 9-port performance and if you want to go real crazy you can mount a (modded) 5-port P/S set into a 9-port engine.
It would be better to say a single exhaust port engine to rule out all faster motors which always do have a multi exhaust port.