400 intake on 333 heads
The 400 horse intake has much bigger ports than the 333 heads. It can be done, but it isn't right. You will be feeding a large port into a small port. It will work, but sure isn't efficient. The bolts over the ports are raised on the 400 intake, and won't bolt to the 333 head. some have done this, though. I think you also have to machine the top of the intake where these bolts go, as it will hit or interfere with the valve cover. Sealing the top of the ports is also a problem, as there are no bolts there due to the misaligning.
You would be wise to either find the bigger heads, i.e. 690 or 583, which are pricey, or use a 340 horse intake on your heads. Any low performance intake will adapt or bolt up to your 333 heads, even a tri power or Offy dual 4 bbl. I would hesitate trying to do the 400 on your heads. JMO.
Fred
