Thanks for the ideas, fellas. I have the tall Cobra valve covers from Performance Unlimited, so that's not it, unfortunately. I did look to be sure after your suggestions, but I found no scrub marks. I was hoping I would, though.
I went to a local performance shop today and he felt the best explaination would probably be defective lifter(s). Especially in light of my recent bent pushrod. He checked the preloads and felt they were fine.
Wierd thing happened though... Check out my carb jetting thread.