Locked Up!, What might it be? Options

[74914LE]

Just finished getting a 72 1.7ltr. ready to start up after sitting for 29 years. Went over everything in the fuel, vacuum, and ignition systems. It turned over just fine without spark hooked up to it. Now for the moment of truth. Made sure I had fuel pressure and attempted to start it.

After about 3 tries, it fired up and started running!!!! After about 20 seconds, a rattling sound started, then got worse. I immediately shut it off. Then tried to turn it over again, and it would not turn over. I then got it on jack stands and blocked one wheel to put it in gear and see if I could spin the motor by hand with
transmission in 5th gear. The wheel will turn about 1/3 a turn in either direction and it locks.

Before I drop the motor and pull it apart to check for a dropped valve or worse, though I would see if anyone wanted to weigh in on what this might be....ideas?

Thanks in advance!

[74914LE]

Pulled the head, and it was the valves that were seized in the guides. The damaged looks to be contained to the push rod. Probably the thing bent when it was turning over prior to starting. When it started on 3 cylinders, that is when the
noise really kicked in, and the extra force bent it to the point that it cased the cam follower to press up against the cam to the point it would no longer turn over. Once everything was off, everything spins like it should.

Took the head to the shop, and we took them apart. Had to drive the valves out with lots of force. Hopefully by the end of the week, everything will be rebuilt, and with a new top end on the motor, we should be back in business! New set of rings as well.

Thanks to everyone for your comments. It is always an experience to find out what happens with these cars. Based on what I saw, it looks like the previous owner ran it for too long with a bad thermostat, and the MPS was also on its way out. The extra moisture, combined with the extra carbon from running rich, was probably a huge part of the problem.