Straight steerer 1 1/8 fork in tapered frame

To get a straight steerer 1 1/8 fork to work in tapered frame (which has a 1.5" lower cup/bearing) you need a Crown Race Reducer.

You use the crown race reducer in place of an ordinary 1 1/8" crown race.

If you need a new headset, then you can get a ZeroStack Conversion Bottom for 56mm Head Tube.