I emailed Lunt to ask them. I’ve had a very helpful reply. The summary is:
“You cannot simply take a pressure-tuned etalon from one 60 mm and insert it into a tilt-tuned 60 mm — they are not plug-and-play. If you want pressure tuning, the safe path is a factory retrofit by Lunt, or purchasing a PT model outright.”
It is all to do with spacing, and alignment.
James