The '69 and earlier heads had the oil come from a small passageway in the block, up to the rocker shaft/rockers. The '70 and later engines had the traditional pushrod oiling.
You can easily convert the older engines to run a modern oil thru pushrod setup. Plug off the holes in the block/heads and use the '70 & newer stuff. Alot of BBB guys like to use the earlier heads....especially if the run in a class that doesn't allow porting.