Having done this last week with Highlander..it'* all very very fresh.
The gasket for the upper is a plastic frame type and has clips that hold it to the upper intake itself. Here we have AJ holding the intake w/gaskets clipped on. (No..he doesn't model on the side..this is only a weekend gig for him
The "hidden" bolts, there are two of them, they are not part of the upper intake manifold. They are at opposing corners of the lower intake manifold. Front driverside and rear passenger side. This picture shows the rear passenger side. Under a little water/coolant
Here is the ratchet, extension and deep socket (3-4") on the front driverside hidden bolt.
Lower intake full of water/coolant
Upper intake wet from the failure
Some tips. When you get the upper intake off, get most of the water out of the lower intake before removing.
Double check amount of injector o rings per package. They are typically packed with 4 rings per box. Hence your need for 3 boxes.
Have 3 cans of brake cleaner and 1-2 of air intake/TB cleaner on hand. Brake clean removes all oil and residue from gasket areas.
Spraying a light amount of silicone lubricant at the injector o rings before you try to remove the fuel rail helps them loosen up and come out.
Take your time and clean all gasket surfaces well.