When you install main bearings and rod bearings the bearing caps need to be positioned correctly to avoid it binding up.
The tabs on the rod bearing caps should face opposite of each other when installed.
Also on the main bearing caps make sure you're placing them back in the correct position as well by the numbers.
The main bearing caps should be numbered as in 1, 2, 3, 4, etc and the main bearing caps will have arrows on them as well.
The arrows on the main bearing caps should face the front of the engine when installed correctly.
If they are installed in the wrong place or not facing the right direction then the crankshaft will bind up and be really hard to turn.
When I rebuilt my first engine is was a learning experience and I had to redo the bearing caps and rod caps about 5 times before I got it correct.
Still it was fun though and now I have no problem rebuilding motors and putting the bearings in the engine properly.
A crankshaft will also be a little hard to turn over at first but you should be able to move it with a cheater bar or use a pipe wrench on the crankshaft with a rag around it.
The way I turn my crankshafts over instead of using a ratchet is to take a cloth and wrap the front of the crankshaft where the harmonic balancer goes with a rag to protect the crankshaft.
Then use the pipe wrench with a cheater pipe to turn the engine over.
The engine then usually turns over without very much resistance.
A little resistance and friction is normal on the crankshaft turning but you should be able to use a pipe wrench with a pipe with more leverage and turn the engine completely over.
You should also remove the spark plugs to remove the compression that puts up a fight as well when you just rebuild a motor or put new main and rod bearings in.