340 GURU needed

Well a long story cut short. My 340 quit running! Seamed to be locked up. Had towed home. Crank will turn 360 degrees then stops ( more of a thump a than a clank!) . Took starter out, then took valve covers off to check for a dropped valve, then unbolted torque converter, then pulled distributor, then oil pump shaft, then pulled fuel pump! And dang! It still will turn 360 degrees then stops cold! won't go past that spot.


Also pulled plug and felt the top of all pistons. Stuck my magnet in each cylinder to se if anything came out! Nothing!

What's next?