340 seems to be locked up

Last it moved freely was while connecting torque converter. So that’s where I’d go back to. Flexplate installed properly, meaning front and rear. Proper bolts in torque converter to flex plate, if they are not correct the bolt head will catch on block. Was the converter properly seated onto trans shafts, this can be a bear because there are two sets of splines that are engaged. If the flex plate is installed properly then you should of had to pull converter forward to bolt it up if the converter was properly engaged to trans.