Is the engine upside down?
If so, turn it the right way up and try to crank it over again

I had a similar panic with mine a few years ago, i fitted the oil pump and it went really stiff (Oo-er). Turned it the right way up and it rotated smoothly. Fuck knows why. Must have been something to do with the oil pump.

Also, some CVH's came from the factory with oversize bearing shells IIRC- so if you have refitted standard ones they will be tight, and useless!