hi, being that you have some loose rockers and the oil pump isn't getting oil to the top off the motor and the rotor doesn't turn .
I would check the timing chain and marks .
it could be that the 3 lifters are pumped down and the dist gear is stripped or broke the shear pin that holds it to the dist .because of a bad oil pump.
I would advise to pull the distributor and see if the shear pin is broken and also, see if you can turn the dist shaft while holding the gear .
this was a common issue with these motors .
it may be that you have a bad oil pump and dist gear .
it could also, be that the gear pin is bad and that three lifters pumped down because of it .
I would first check the dist gear and also, the rod that goes into the oil pump.
once you have the dist out see if you can turn the rod that goes into the oil pump ,you can use a 1/4 inch ------5/16 socket with an extension to do this .
if that is good .then inspect the timing chain for slack .
the tensioner may have gone bad and the timing then may have jumped
usually the timing chain broke or jumped if there are loose rockers ..
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