The intakes are single plane for 4150 style Holley, and single plane with Dominator carb pad.  The intake manifold on the right( in the picture above) is a single plane 4150 that I ported after I got back from the 2019 EMC for testing on the 303Y where it made about 12 extra horsepower.  I wanted to test it on my 375 Y, and I have been waiting on the opportunity.  There is a big difference in horsepower on a well built engine over the dual plane intakes.  There was a 13 hp difference in the 4150 style carbs, and 30 hp difference on the 4150 single plane with the Dominator and super sucker on the 375Y.  With the single plane Dominator and tunnel ram, there was a 35 hp difference on the 375 Y.  

JDC