We've had several people bring freshly built engines to us that were hard to turn---most had been assembled with some thick goop ---generally cleaning the bearings and putting them back together with 5-30 they would turn easy

If you want to get into it---turn it upside down, take off the pan and take the rods loose and push the pistons to top of bore---see how crank moves then---take mains out , remove crank, clean bearings, measure clearance, put to gether and check for free movement after EVERY main ---if all goes well with mains , do the same to rods, clean, 5-30, torque , turn( you won't be able to turn completely over , but you can turn some---also make sure the bearings are right size for crank---if this doesn't resolve the issue, and you want to go farther , take it all the way down and fix whatever is wrong