possible solution
I remember having the same problem a few years ago with a cannondale bike/frame. I wanted to put the hanger right on top of the headset, but the headset was too wide and hit the underside of the hanger. I solve the problem by taking a dremel and grinding away some metal on the underside of the hanger (the one I was using already had a curved cutaway underneath the hanger arm). It didn't need a whole lot of metal removed. Depending on the size of the top cap and hanger you may be able to do the same.
sorry for the poorly worded explaination.
jhr
I remember having the same problem a few years ago with a cannondale bike/frame. I wanted to put the hanger right on top of the headset, but the headset was too wide and hit the underside of the hanger. I solve the problem by taking a dremel and grinding away some metal on the underside of the hanger (the one I was using already had a curved cutaway underneath the hanger arm). It didn't need a whole lot of metal removed. Depending on the size of the top cap and hanger you may be able to do the same.
sorry for the poorly worded explaination.
jhr