In your other post you state that you have removed the intake manifold and I believe the heads as you said the head gaskets look fine so this is a mute point as no easy way to pressure test it now. Send the heads to a shop and have them magufluxed to look for cracks. They need to go anyway for a valve job from what you said about cylinder 4.
1997 2400 SCR
5.7 Vortec / Bravo 2