If you look at the squareness of the counterweights you can tell it's cast, plus, a forged would likely not have broken like that. Regardless, I doubt it hurt the block, but I would replace at least that one upper main bearing on #1. If the motor is stock (factory rods and pistons) another stock cast crank that has never been molested should be close enough in balance. If it bothers you, definitely have the balance checked. Take the harmonic balancer and let them know the rear is also externally balanced. If you have a stick trans, take the flywheel, otherwise you're almost stuck buying a B&M external flexplate.