No Compression

Get the Harbor Freight compression gage set like I have, cost ~$15 on sale. You can use the hose in the kit to connect to an air compressor (standard air fitting). Use that as a poor man's leak-down checker. With each piston at TDC compression, listen & feel w/ tissue for air flow from the PCV valve hole (w/ oil fill hole plugged). That would be bad rings. The only other places to leak are to intake or exhaust, other than to outside via a bad head gasket. It seems inconceivable that a bad head gasket could take out 5 cylinders.

The timing dots don't usually line up at TDC #1. It was TDC #6 on my small block. I forgot about slants, but you can read up here. I can't recall a way to put a timing set on wrong and still have the dots line up.

Before I started tearing the engine apart, I would try to run it. Even before that, I would turn it over by hand. If you feel 3 strong "air springs" in 2 crank revs, the engine is good and your compression testing method is bad. You can turn most slants over by tugging on the alternator belt.