FE's are a whole 'nother animal when it comes to sealing the intake manifold. The first issue is that the intake gaskets are always going to be under oil. It's not a situation like a SBF where the intake gasket/intake manifold flange is just susceptible to splash from the valley. On an FE, the intake gaskets are susceptible to all the oil raining down and draining from the cylinder head area.
Intake manifold geometry is very crucial. If the flanges are not on the correct angle, it will allow for a gap, which will allow for oil to be sucked in.
Yes, the head gasket tabs can hold an intake off the head. That's a very common problem and it's pretty much SOP for me to just knock them down.
If you're swapping intakes back and forth and still experiencing a problem, I would make sure that the tabs are not holding the intake up and I would make sure that if you're using cork for the china wall gaskets, that they are not too thick. That would hold the intake up as well.
When I install an intake, I first make sure that the angles are correct and the intake doesn't need to have the flanges milled. I then silicone the intake gaskets to the heads. I also don't use cork, but I use the silicone instead, so there are no issues with the cork being too thick or thin. I also use another layer of sealant on top of the intake gaskets and then install the intake manifold.
If you think the valley pan is giving you fits, then you can just leave it out. However, you need to at least double check that it's not causing an issue by holding the intake up.
Here's a pic of the head gasket tabs being knocked down on an intake gasket mock-up....
