34 Flathead only turns about 45 degrees then catches

[Robbo]

I have a 34 Ford Phaeton that I am working to restore. When I turn the crank, it will only turn about 45 degrees then stops with what sounds like a thud in the front left of the engine. The wiring is completely out of the car now, so no use of the starter. Heads are off as I am cleaning all the accumulated gunk out. Cylinders and pistons look good and move freely for the little bit that the engine will turn. Any ideas what might be holding it back?