Broken or missing piston rings will allow air to bypass from the combustion chamber into the crankcase, which you could here thru the oil fill.
If you can also here air escaping into the intake manifold, and all rockers are off the valve stems, all I can think of is there are bent valves not sealing correctly or the heads are badly cracked between the chamber and the intake port....have never seen that happen on an LS.
Is this the same engine that has all the oil issues in the intake?
On the bad cylinders, 2,5 and 8, remove the pressure feed attachment, squirt some heavy oil like 90 grade into the chamber and retest bypass...
