odd crossover ports in early dual plane holley?

That is a Duntov crossover design from the old Chevy days that Holley crossed over to their line. See the 2 blank holes on the rear in the crossover valley, that is EGR. One side is plumbed to blind ;intake' hole, the other is ported to exhaust crossover. The 2 smaller holes are the threaded mounting holes for the EGR plate. You can run it as is as there is no physical connection between the exhaust and intake plenum. I think that design is called a 180 as it only draws from 1/2 of the carb, as opposed to the open plenum Offy "360" design that pulls from all 4 barrels. Probably a torque theory thing.