The blue Pocketbook just deciphers the chassis code but doesn't say which rear spring is for sedan or wagon. No mention any HD spring. So below is what I could gather from the web:

Spring #1359710 is for 740/940 wagon conversion from Nivomat which had used spring #1273977. Spring #1359710 have thicker coil than #1273977. Both springs have 400mm uncompressed height. Spring #1273977 may be softer and have lower ride height but compensated later by Nivomat.

Spring #6819404 is for HD use sedan/wagon with thicker coil (thicker than springs above) with lower 380mm uncompressed height. Its harder to compress but when the car sits down the ride height would still be in specs.


Hope these helps,
Amarin.