Depends on the fans. Most 120mm fans won't have mounting that'll line up with the 140mm mounting holes on the Rad.
Some Noctua offerings are 120mm's utilizing traditional 140mm mounting points, and I'm sure adapters/brackets exist for others....
I guess the question would be, why? If you have room for the 280mm Rad, you should have room for 2x 140mm fans.... which (should) run quieter than their equivalent 120mm offerings....