Edelbrock Head Rockers?

Run what ya got IMO.

The closed chambered heads that were mentioned to you are the other "LA" heads and not the Magnims. And yes, if you go with the Magnims, you'll need to send the rockers back.

The other Edelbrock heads have a few less cc's because there is no machined area for the 340 pistons that come up above the deck height. If your 340 pistons come up out of the block, then you have the correct heads.

If they do not come up out of the block, then You can used the slightly less cc head.