I've been restoring my 68 coronet for the last few years. A couple of years ago i bought a freshly rebuilt 64 block 383 motor to put in it. The motor was close to stock, with the exception of a mopar purple cam, and a few bolt ons. I dropped the motor in about a year ago. I bolted the motor plate to the flywheel, but haven't done anything else to it since. As i have been working on the rest of the car. So a few days ago i added 5 qts of oil and a bottle of lucas break in zinc additive. Then i pulled the dist & intermediate shaft, and primed the oil pump. Next i put a socket & breaker bar on the crank bolt , to turn it by hand. The engine turned just slightly and then felt like it was steel jammed against steel. And wouldnt turn any further, even with considerable force. I turned the ratchet backward a few clicks( less than one full rotation), and it seemed to be moving ok. But as soon as i go forward again, and reach the same spot, it binds up again. I pulled the valve covers but saw no signs of bent rods, broken springs etc. Next i sprayed wd40 in the spark plug holes and tried turning it back n forth. It pushed the wd40 out of some of the plug holes, but stopped rotating again at the same spot. The car is an automatic. And the trans was rebuilt before installing. Theres no trans fluid in the trans yet, but i did check that it was in park ( tried nueteal too). Could this be a seized piston, stuck valve, or stuck lifter ? Or a clearance problem with the rotating assembly ?