I needed to modify one spacer to match with the headset cover, but other than that, it all worked well and provided a smooth finish.
The reason for the modification was that the headset cover on the newer TCRs (1 gen removed from the newest full-internal model) had a rise at the back (see image below) to integrate smoothly with the curve at the back of each headset spacer, which in turn perfectly matched the curve of the stem.
Assuming the cockpit you want won't have a curve at the back of the stem, you'd presumably need to modify two spacers - one to flatten its bottom to work with your headset cover, and a second to flatten its top to match with the stem... and that's assuming the stem would have a bit of an extension after the bolts to match up with the extension of the headset spacers.
That would also mean running at least 15mm of spacers, in order to have space for the sanding / shaping needed.
Honestly, it may be easier if the cockpit company has their own headset spacers, which are made to match the profile of their stem clamp area.
