I have several, bear with me.
I have a Leakless w
The A-8502-A pump has a seal system in the rear bushing. The pack nut appears as the original.
A sealed ball bearing is used in the front of the pump which is out of sight
when the fan is installed. The ball bearing is an advantage if you are going to install an alternator. It will take the side load needed to keep the belt tight on the alternator.
The original water pumps used a needle type bearing that is not as durable.