Not sure that it would matter since its going to drop anyway, but GM specs a 20-25 psi startup when using the Kent Moore pressure bleeder. Also, here’s their diagram showing that clip on the combination valve during bleeding.
My 98 truck had a lousy pedal about ten years ago and I damn near put a “for sale” sign on it. It, too, was supposed to be a one hour effort. What a pain in the ass.
I accidentally fixed it when replacing the booster a few months later. I left the MC connected and tilted it down for clearance while I did the swap. I guess some elusive bubble found its way to the sky when it was jostled.