remove the spark plugs?
Sometimes when you are turning the engine over by hand and you get to the top of a compression stroke it can be VERY difficult to turn it further.
A bigger breaker bar on the crank nut will help
BUT
before you do this I want to make sure you stabbed yout TC properly, twising it as you push it back on the input shafts and pump drive. I usually mark the front of the converter on the side of the bellhousing so after I rase the trans I can make sure the converter sits fully back during the entire install
The TC when fully seated on the input pump shaft will have about 1/4"-1/2" of room behind the flex plate, meaning when you install the first of 4 TC nuts the tc should pull forward almost 1/2" into the flex plate.
If not then you may have the converter not fully seated, bolting up the bellhousing with this can damage the converter and more and cause everything to bind.
The fix is to loosen the bellhousing, drop the trans again and ensure the converter is FULLY SEATED
Dont ask me how I know
Also make sure the trans is in N