I would also check the rocker shaft, this can very easily be assembled incorrectly when stripping down a rocker shaft assembly and could be fitted in the wrong orientation, (an old trick to raise oil pressure when selling a duff engine) (not saying your is). On the original rocker shafts there is a line on the end of the shaft (as stated in workshop manual), but newer replacement parts do not have this mark and you have to work it out. It is important because this lines up the oil holes to allow oil to flow into the rockers oil tube and into the cup, makes a cushion around the ball on the top of the push rod and the rocker cup, engine will make tapping noise if not getting oil in there ie not lined up, Just a thought anyway!
On a second note, I have never measured pre load unless building a performance engine, hydraulic lifters pump up at hi RPM and limits max RPM, I have only used adjustable rods when using solid lifters along with some unsociable cam, but then you need to machine valve spring seats down a bit, plus many other knock on effects (all depends on what is required of the engine)
