66ford298:
No flame intended but lifters in the case of the OHC are more properly called lash adjusters. (You don't want the pushrod mob to get upset!) Lash adjusters can and do get tired and can be replaced. The tensioners used to be cast and are now plastic and they (either type) can get tired, too. If the noise is coming from the front of the engine, then replace the tensioners. And the guides, if the mileage is high (>100k). You don't say whether the car has aftermarket cams but they can push borderline lash adjusters over the edge. With the screwdriver/stethoscope, you should be able to pinpoint the area where the ticking originates. One final note, if there is a lot of gunk built up then it is possible that the oil supply to the lash adjusters is not 100% or the lash adjuster innards are partly plugged. Either way, the adjuster doesn't work as intended, resulting in noise.
HTH,
Chris