I suspected you were doing something similar. The simple and complex answer is no. You need to design your frame one of two methods. You either find a Cannondale Headshok headset from a Cannondale bike and use that, then have your frame built to accept the Cannondale headset AND make the frames headtube the same length as a Headshok framed Cannonadale. OR, you find a Cannondale headset, removing the sealed cartridge bearings from the headset cups, and design you headtube with the proper dimension from the lower bearing to the upper bearing and machine the headtub for an internal type headset.
From experience with a lot of Headshoks, you will be better off finding a Cannondale headset.
The reason for all of this is that a Headshok steerer tube is not the same diameter over the entire length. Some possibly on the older Headshoks, but the newer ones are stepped very slightly to make removal and installation easier.
Also consider that when removing a Headshok from the frame, the lower headset bearing in a proper unworn Headshok will have the headset lower bearing stay on the frame. So if you machine a new headtube, expecting to make it an internal headset, the fit needs to be such that it is not a tight press nor loose fit.
If time permits in the next day or so, I will get a photo of a steerer tube.
Not sure of your frames details or which Headshok, but you may be better to consider either cutting up a frame and reusing the headtube, or better still is finding a Merlin Fat Ti. The Fat Ti Merlin I have experience with and will say it is one of the best hardtail bicycles I ever rode. Regardless, the Merlins I built for riders, and even the Headshoks we still ride in this house have modified internals and spare damper cartridges since they are a constant maintenance item if you want them at 100%.
PK
From experience with a lot of Headshoks, you will be better off finding a Cannondale headset.
The reason for all of this is that a Headshok steerer tube is not the same diameter over the entire length. Some possibly on the older Headshoks, but the newer ones are stepped very slightly to make removal and installation easier.
Also consider that when removing a Headshok from the frame, the lower headset bearing in a proper unworn Headshok will have the headset lower bearing stay on the frame. So if you machine a new headtube, expecting to make it an internal headset, the fit needs to be such that it is not a tight press nor loose fit.
If time permits in the next day or so, I will get a photo of a steerer tube.
Not sure of your frames details or which Headshok, but you may be better to consider either cutting up a frame and reusing the headtube, or better still is finding a Merlin Fat Ti. The Fat Ti Merlin I have experience with and will say it is one of the best hardtail bicycles I ever rode. Regardless, the Merlins I built for riders, and even the Headshoks we still ride in this house have modified internals and spare damper cartridges since they are a constant maintenance item if you want them at 100%.
PK