Early 80's 305, with CCC or CCCC Computer (or not), 8 Degrees static . Hook the advance unit back up , Manifold source for power, ported source for economy and smog..
Detonation sounds like marbles being shaken in a can..occurs usually under throttle load, and uphill pulls..Being that far advanced will probably make it run a bit hotter than normal.
After you set it for 8 degrees , take it on to the freeway, going up the ramp..Hammer it..If it pings / Rattles.. retard it. If it barks like a dog, advance it a bit..
Don't know what to tell ya about turning the engine over by hand with no valve action..but that doesn't sound right..maybe with a socket and breaker bar..Do a Vacuum Check .. 17 to 21 In Hg and STEADY, Bouncing Rapid Needle indicates burned/Leaky Valves, Guides, or seals..
Do a Compression, 125 to 150 PSI + / - 10% all the way around is good..much lower think rings/ rebuild.
Did you break in the cam properly ? 2000 RPM for 5 to 20 minutes?