Hmmm, maybe I can clarify.

The head tube is larger than 1-1/8", but is made to accept a Campagnolo Integrated Headset which by definition has a 42mm outer bearing diameter. These bearings fit directly into the head tube without any external cups as they are already specified within the head tube itself. The inner diameter of these headset bearings are spaced to fit a 1-1/8" fork steerer tube both above and below.

I was thinking that the lower bearing, still using a 42mm outer diameter to allow it to be used within the head tube, however instead of the inner diameter supporting a 1-1/8" it supports a 1-1/2" tapered fork steerer. That's 38mm by my calculations so the inner bearing diameter is 38mm and the outer diameter is 42mm. That only leaves 4mm for the thickness of the bearings, but maybe that's possible.