Set the intake gaskets on the head and use some Gasket Cinch to hold them in place and then install the valley pan loosely to see if it fits snugly or has a gap between the gasket and pan with the intake manifold place on top of the pan
If it is loose try adding the other gasket on top of the pan, if it is tight with one and the manifold bolt holes look like they are near the top of the valley pan remove the gasket and see if that fits better
Every motor is different so you need to check the fit and use what fits the best