It actually sounds like you have two seperate problems, as far as your plugs oiling up this is either excessive valve guide wear or lack of seals "which as you said machinist has checked" or collapsed oil rings/incorrectly staggered oil rings/lack of a honed surface on the bore. As far as oil everywhere up top and when you pull manifold of its oil everywhere, where exactly are you talikng about on top sides of the gaskets/bottom sides or centre of gasket, if its topside then recheck rocker seals and have a good look along perimeter of manifold for any small holes from head manifold mismatch, I had a holley manifold/pro topline heads and they mismatched by a mm just behind the front water passage, when you gave the car a gutfull there was oil everywhere but couldnt work it out until I had a really good look, if its oil under the manifold thebn thats fine, if its oil on the mating suraface then thats a new one to me, hope this helps
Steve