You were wise to be gentle with the fan cage while removing it from the old motor and installing it on the new one. It is brittle 20 year old plastic. I've seen them heavily encrusted with caked on dirt. If yours is like this, it is a good idea to wash it while its apart. Note that there may be one or more small balancing clips at various places on the cage. You want to avoid dislodging them. When installing the cage onto the new motor, don't just drive it on with a hammer if its a tight fit. This can damage the bearings. Instead, sand down the shaft until the cage slides on with a moderate amount of resistance.

Is the 87 Celebrity the only GM fan that will fit a 740? It seems to me that this part will likely soon become unavailable---discontinued due to low demand. When was the last time you saw a Celebrity on the road??? I see a lot more 740s nowadays---the Chevys just don't hold up like a Volvo.