[boxhead]

lifter noise is more like a ticking sound and it is at half engine speed as they are driven via the camshaft.
is the noise there at idle? or is it only at a certain rpm range?
does the noise only come when driveing the vehicle? ie under load
it could be camshaft or crank end float?
just tossing ideas around as it is very very difficult to diagnose engine noise with out hearing it.
if the noise is there at idle try droping the box out and run the engine, atleast if the noise is still there it is deffinatley in the engine