I have seen nitrous plumbed like this also.
Whatever the purpose you need to keep the tubes away from the carb linkage.
The pantera linkage is a little different since it needs the center pedestal so the accellerator can pull it.
That doesn't leave much room for the vacuum tubes.
The first few batches of Hall manifolds all had a 1/4npt hole on the valve cover side of intake port #8.
That is where I get the brake vacuum and vacuum advance from. Is it scientifically correct? Probably not but it works well enough. I try to leave well enough alone.
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