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Making a base for a different fan height is no problem at all. It can be cone with just a few clicks. What diameter would you need? 70mm or 80mm.
About the 120mm fan things get a little complicated because the outer part is not meant for such large fans. I think the bes solution would be making a base for a 120mm fan and then an adapter from the 120mm base to the 80mm outer part. I think this is possible, but not useful. I would even say that the 80mm fan is a little bit oversized, because a larger fan does not necessarily correspond to a larger airflow. The pressure is the limiting factor here and I think a 120mm fan does not create a much larger pressure than a 80mm fan.
However if you need a different size, please tell me both the height of the fan and it's diameter.