When I rebuilt my 340 engine with an Edelbrock LD340 manifold, the Fel-Pro gasket set cork gaskets at the front and back of the block were too thick to be used. The dual beads of Permatex do not seem to be sealing properly at the corners.
The PCV system seems to be working fine.

Does anyone know if there are better seals for the front and back of the manifold?

Did you remove the locating dowels from the rear rail of the block. If not after market intakes will not sit down properly and will leak.

Yes. I did remove the dowels. I probably had about 0.125" clearance and the cork gaskets are 0.180" thick.

I have never used the end rail gaskets always use just sealer

Using sealer is the best approach. Pull the manifold, clean the surfaces then wipe them down with Brake Parts Cleaner and clean paper towels to remove all oil residue. Then set the side gaskets in place (I use glue to hold them in place) and temporarily set the intake in place. Note how much sealer will be needed and remove the intake. Cut the tube's applicator cap to the next size larger and carefully lay a nice bead right across and slightly up in the corners. Take note where the sealing surface is because its not straight across, especially the passenger's side front. Carefully set the intake in place and bolt down. That should put and end to the leak.

Thanks..Sounds like a good project for this weekend.

If you can let it sit over night before starting it that would help too.

I have the same setup on my 340, I used the cork gaskets with sealer on each corner and it has never leaked. I just got the bolts started and pulled them all down. Good Luck! Ronnie

I still have the install instructions from my
Eddy intake and it specifically states to not
use the cork gaskets at all and use silicone
to seal the intake. For what it's worth.

My Mopar M1 leaked like crazy with the end gaskets,
so I discarded them when I installed the Eddy intake.

Due to machining and/or tolerance variations (particularly with an aluminum manifold), going with an all-sealant scenario is generally best. The cork and sponge seals can shift and deteriorate. You may also want to consider some sealant on the bolts, as oil can run up the threads. When installing the manifold, especially an aluminum one, torque it down slowly and evenly from the center and work your way to the ends. Recheck after initial run-in and cool down.

Bill Rolik