I've done a bit of research and then some contemplation (scratching my arse whilst thinking). The termi headers are the same diameter, but have 1 times diameter bend top and bottom, whereas the OEM have a 1 times diameter at the top and a 1.5 diameter at the bottom. I am also of the impression, but may be wrong, that the OEM headers are a little longer toward the back of the bike than the termis.
I'm not overly experienced with this shit, and I'm not sure what the impact would be by using OEM's on a Termi system, but my head is ringing alarm bells around tuned length, hence resonant pulse frequency's, and then impact on VE (volumetric efficiencies.)
If I was to pick up what is left of this system it may look nice, but may be worse than the OEM. Not sure what to do...
Regards, Greg