Promax sells a nice cast cover with seal for $100 but you'll need to add a pointer. It fits under the waterpump. You need to trim back the oil slinger if you're going to use one as it will rub the cover.
Ok, I got the name wrong and can't remember who they were - they were at the Indy swapmeet. Anyhow, Muscle Motors sells the same one so try those guys. They were a few bucks more and didn't include the seal.
They're a nice piece. I drilled the hole and put the plug in so I could check cam end play. The cover is thick enough to tap.
