Please post the results.
I see the steam port is drilled in the back of the pump housing inline with the water outlet. That puts it well below the height of the top of heads. Its not immediately obvious to me this will let vapor escape. But Holley must have sold some of these and know how they work. ?
GM went to the trouble & expense of running a hose from steam ports UP to the top of rad. For peace of mind this is what I'd do, either direct to rad or into a tapped rad hose coupler.
steam port on Holley
location relative to heads
It is not just a matter of burping bubbles from coolant at refill but of letting steam out if it ever starts to boil, otherwise the heads just keep getting hotter