Yes you need a custom header for that block. To be honest with you, I have never seen a wedge eared Hemi block running. I personally mocked up a set of headers on one of those blocks and there was no way in heck that you would ever to get that to work correctly.

Buy a standard Hemi block with Hemi mounts and run a Schumacher (206-364-7151) engine mounts and call it a day.

....there is nothing like driving my 1968 Hemi Dart around town and having people looking at you like you're nuts!!