make sure to use rtv on both sides of the gasket when sealing the intake mankfold, also make sure the manifold is straight and not tapered.
If u could seal off the water cross overs and then pressure test the the cooling system with intake off and see if water is coming fron the int oorts, that would be great...but its mote likely the gasket leaked from lack of sealant and or manifold taper.
jmo