My main concerns would be rust, depending on where it's from and the wiring harness and head gasket. The head gasket is pretty much maintenance on the 104. Not a deal breaker. I wouldn't worry about the the chain or any of the valve work mentioned above. I've seen plenty of these with high mileage where the valve terrain looks perfect. Besides, it wouldn't be too cost effective to spend that kind of money on the engine when a used 104 motor is almost free.