[Closed] Cannondale Prophet Headset

Hi. I have just got my hands on a 2nd hand Prophet and believe that the headtube takes a 1.5 headset. At the momment the frame has the deeper bottom headset cup which is recommended by Cannondale to prevent the forks fowling on the frame downtube. It has a FSA Orbit, 1 1/8 headset fitted but requires replaced. As I am building the bike up with some new parts I was hoping to take advantage of some of the discounted deals for 1.5 forks on the market, but can't seem to get info on what headset I could use. Does some 1.5 headsets work with the deeper recommended Cannondale headset cup or can I remove it and replace with another headset lower cup (Standard) without new forks fowling the frame. Not sure if 1.5 forks are not suitable for my intentions and should plump for a 1,1/8.

Any advice would be greatly received. Thanks. Whistler