Balance Issue / Vibration

Yes, it's very possible. I've seen it may times. Unfortunately, I don't know any way to tell if it cast or forged short of pulling the pan. Maybe if you had a camera that fit down the dipstick tube or through the lifter valley down into the pan you could see but I've never had the equipment to try that. You can determine the year of the block by looking at the date code but that's no guarantee it has the original crank.