Replacing a valley plate in the car with the heads on can be tricky to get a leak free installation. I would just replace it with a factory type bathtub gasket properly sealed on the ends. Otherwise you will need to cut the old loose from the heads and try to remove ALL the sealer from the block and heads. If you do decide to install a billet valley plate go for the one with the removable plate so you can access the lifters if you need to. Like Andy said you will need to remover the heat crossover on the bottom of the intake manifold. I had to do that on my 493 with an Indy valley plate and Performer RPM intake. It's a big messy job and hard to apply the sealer evenly unless you remove the heads. I'm not 100% sure you can use a valley plate alone to seal with Eddy heads without some kind of filler plate like the ones Andy sells called "bat-wings"
Gus