I recently replaced the top end, minus cam, on my 64 326 2bbl.  I had a lifter that collasped on the passenger side.  I replaced all lifters, rockers, and pushrods.  I also checked all the lobes on the cam and they were fine, no visible wear at all.  I now have a tick from the driver's side rear that comes and goes but is there more times than not. I have scoped all the rockers, left and right bank, while the engine ticked and they are quiet.

Any other suggestions?  

Sounds like an exhaust leak or heat riser but it is on the passenger side. Could it also be a rocker stud is pulled up or a broken or weak spring??