We had a customer bring in a Giant XtC SE 1 mountain bike frame that was to built up with parts from a completely different bike. The Giant XtC had an integrated headset, but it was not built into the frame. It was a piece pressed in.
So, we put them into the now empty headtube. One on top, one on bottom. Kinda reminds me of some Star Wars device.
I’m posting this because I couldn’t find anything helpful online. Hope it helps someone:) Remember to have your local bike mechanic perform this!!