This killed me last night so i dug a little further. I actually have to go look at some of my blocks and see if there is any difference in the location of the oil hole to the head in the deck of the blocks. That is, is there a difference in either the placement or size of the block deck oil feed passage. If there is not, then it would appear that the difference lies in the head and the rockers. So, the heads starting in 59 apparently got a new drilled passage so if you are using a 55-57, and possibly 58 head on a 59-62 block, you may not get oil to the rockers, or enough oil to the rockers. There apparently was a special bolt that was drilled from the bottom up to just above where the threads ended and then cross drilled. This was done to the bolt near the oil tube pick up on the head. near as i can figure, this was done because the later blocks put more oil pressure and volume to the head and using an earlier head restricted this pressure and volume. The later motors also had the return loop on the rocker connector pinched off to keep this higher volume and pressure in the rocker shafts.
The 59-62 rockers are slightly different too. I have two new sets, one trw and the other sealed power. When you look in the hollow of the rockers, you will see that the oil groove is offset and does not intersect the oil hole that feeds the top of the rocker arm to drip on the valve stems, springs. When I pulled out a box of filthy dirty 55-57 rockers, those had the oil groove centered in the hollow and intersecting the oil feed hole. the best I can figure, was that GM wanted to solve the rocker oil feed problem from the earlier motors (you may remember the copper line and restriction valve kits that feed oil from the oil sender output or oil filter output to the side of the head)by putting more oil and at a higher pressure to the rockers, sealing the loop off, and making essentially a pressurized system. the offset groves must be to limit the amount of oil that would spit out of the rocker holes, with this now pressurized, so to speak, system so if the groove was to intersect, there would be a lot of oil spitting all over the place instead of trickling down over valve train to cool and lubricate. So it seems that if you are using a later block with an earlier head, you have to use a pinched off connector, the later rockers, and double check whether the rockers are getting oil pre-startup and if not, you may have to drill the bolt near the connector tube pickup at the head. Now the next question seems to be whether the later rockers, with the offset grove, can be used on the earlier head and earlier block. I think so because I think i have been using them for a number of years because the 55-57 versions have not been available new for a lot of years. Those are my thoughts anyhow. I have no pride of authorship here so feel free to correct me if my thinking and research have lead me astray.
