small block chevys some times have a problem oiling the front of the engine, did you rebuild the engine? or is it stock? the oil pump might be giving up a little and not pushing as much oil as it should to pump up the front of the lifters on the #1 and #3, or you got some crud blocking the push rods and no oil can make it up them. are the lifters getting oil? or not. i hope some of this helps you out.

Cd