Kill me now, please.

I am hearing that you installed the motor and you installed the trans with the converter seated. Now you are attempting to turn the motor over to align the flex plate bolts to the converter, and in doing so found out that the motor won't turn.

If I am hearing that correctly, then I think the only thing to do is to unbolt the flexplate from the trans and pull the motor and check out the bearings. To me that seems like an awful lot of torque on those main cap bolts to prevent the crank from turning.