question on head exhaust port size

All of them are 360 sized except the <67 antiques. But yes, the 318 has a smaller exhaust port. my 273 on the stand is a 1.00X1.50 and the 360 on the floor is a 1.30X1.70. Thats a 68% or 1.5 inch² to a 2.2 inch² difference in port area. Those are the end ports, the center ports are wider to compensate for the lost corner.