Mark the point along the motor shaft that's exposed under the fan cage. Try to set the cage on the new motor in the same position so the cage doesn't scrape the blower housing.

If you have access to a press or if you can get creative with a jack, it's better to press the motor off the cage than to tap the motor with a punch. The repeated pounding will take a toll on the bearings. Or maybe set the motor shaft on a punch and hammer off the fan.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD