TODAY is a Great Day to visit our Store and order the parts you need for your truck ! ! !
The snout of the torque converter may have some burrs or thick paint that isn't allowing it to enter the crank. You will have to remove the transmission and "test" fit the TC and see where the problems is. You can use some 400 grit sandpaper on the TC snout and smooth it until it fits. I am assuming this is your original TC?
Did you try to rock it forward with a big screwdriver between the converter and trans housing? Sometimes the converter will droop down (play in the bushing).