Diesel engine help

I'm trying to get my Kubota V2203 engine hooked up.  I'm putting it in front of a GM TH350 transmission.  The adapter plate and flexplate from Greg Margison at Overland Diesel are in place and I'm playing with playing with bolting up the torque converter.  I can rotate the engine crankshaft almost one full turn, but then it just stops dead.  I can turn it back around and it stops again as I get back to where I started.  So I tokk the trans back off again, but I can't see anything stopping the flexplate.  Is this normal for a diesel?  The only thing I have done to the engine is replace the exhaust manifold, add motor mounts to the bottom of the engine using the pre-existing, dead end holes, add the adapter to the rear of the engine, and add the adapter to the end of the crankshaft.  Any body got any ideas?   I guess I start stripping off the adapters and hope that frees things up.  I'd hate the idea of taking apart the engine looking for a dropped bolt or something.

Glad it was not more serious. :)

Mine also turned freely when I first got it. It sat on an engine stand for several months. I really didn't try to turn it over until I was hooking up the flexplate and that's when I found that it wouldn't turn over all the way. Again, I had a pretty serious battle with the old exhaust manifold and I will say it was probably my fault for allowing debris to fall in to the engine.

How hard is it to turn over one of these by hand? Do you need a cheater, or you spin by hand on flywheel?

Jay, what a bummer! Finally start turning wrenches and they won't turn the engine. Good Luck.