273 adjustable rockers on 360, very little oil to springs

Definitely revisit the installation of the rocker shafts! If you find that you had installed them incorrectly, you need to remove them, disassemble them and inspect them closely. Look for galling on the shafts and in the bottom of each rocker bore. If there is ANY galling, then you may have major problems. The shafts are case hardened, if they gall it sends shards of hardened material throughout engine. These will take out your oil pump, bearings, crank journals, etc.
if there is no galling, then you are almost golden. I agree with poster who advised to clean oil passages thoroughly in rockers. Make sure shafts are clean inside, also. Of course, also make sure the plugs are in both ends of the shafts.
ZDDP is not the be all end all additive in oil. And more ZDDP is not always better.There are other ingredients, such as moly, which are important, also. Google "rat blog oil", and read it, very informative.