I'm with Mr. Hub on this one.  You can't ride it for months without getting oil to the top.  You will notice something going wrong.  The things Mr.Hub mentioned.  And by the way, the jugs have no effect on the amount of oil to the top.  The difference is in the heads.  So if you are using the 73 head, that's all there is to it.  I personally worry all the time about cooking the top end.  In fact, I have cooked my top end before.  My problem was cheap o-rings between the cases and the jugs and the jugs and the head.  They got hot, fell apart and I didn't have enough oil pressure to shoot it out of the holes onto the rockers/lobes.  The tower bearing were fine.  I too have difficulty seeing the oil in the inspection holes.  It helps if you rev it up.  Hope this helps.  Take it easy.  Julio