Just a thought. Header flange/gasket leak? Thought I had driver side lifter noise on my 340 when I first got it. Turned out to be loose header bolts and blown out gasket.
This ^^ I had the EXACT same noise on my car, sounded like a rocker arm/lifter tick, but I just had a huge header leak, put in some new remflex gaskets and ive never had a problem since. Here's hoping that its not the cam...
