I am looking at the diagram of both regulators and the impression I get is that the only thing they have in common is the 3/8 port O-ring and the small piston O-ring.
Item 15 in the Calypso (2004) is part number 820011 O-ring
Item 6 in the Aquarius is part number 8200-11 O-ring
Same O-ring on both.
The small piston O-ring:
Calypso item 11, part number 820007
Aquarius item 14, part number 8200-07
Those are standard off the shelf O-rings. They HP seat may be similar diameter and height, but they are different part numbers. I have no idea if they are can be interchanged.
Good luck.