[grubsster]

When I had a very similar situation as you are describing I went as far as resetting all the rockers, then I changed all the rockers and pushrods, then I did a lot more research and found that a worn fuel pump or fuel pump rod can cause one to go crazy trying to find the lifter tick. Not to mention the possibility of an arcing plug wire or exhaust leak. I'd do the screwdriver/ extension stethoscope and find the offending lifter also checking the fuel pump drive rod, which was my issue...