Here's another suggestion that I didn't see anyone offer
You said it was very hard to turnover by hand, right?? Or haven't you tried that?? If not, try that before doing anything else I have listed here
Well if it is, loosen the glow plus about 1/4 turn - this will release some pressure on the internals...Try starting the engine again...If it starts, let it idle a little bit, but then tighten the glow plug back up
What happens is the tolerance is soo small for these motors, you don't get enough "free" movement inside with a glow plug fully tightened - I had an OS engine that did this also, so its not something uncommon - BUT once the engine heats up (thus the break-in period) the parts will move around alittle better...
YOu may have to do this trick a couple of times before you can start the thing with the glow plug fully tightened...
Another this is you might want to try a new plug - at this stage and this many attempts to start, the current plug is probably close to being toast...I'd get a MC-59 plug (good general purpose plug) and go from there
But try loosen the glow plug before you throw the thing into the street