Im having some trouble finding a kn filter that fits, with the correct 57 mm in size.. If I use one with 52 mm and a reducing sleeve, would that have any negative effect on performance?

Sorry I should have been more specific. It's not the flange that is the problem, but the size of the filter itself. Im looking for one that is cylindrical and not conical, that Will fit the space between the frame Where the Airbox was

That looks pretty good hondalavis

That was my idea too, but have decided to try and fit a bigger cylindrical filter in the space Where the Airbox was sitting, with a 90 degree adaptor going up to the same original rubber tube as you used.