There's a Youtube video from Cope Racing Transmissions that may have some useful information:
A bit rambling and he pronounces it Bellevue, but interesting to see the different shape of the base of the spring tangs. Also method of measuring play between spring and piston.
What other upgrades have you fitted? I installed the following Sonnax parts:
Manual valve 22771-09
Lube regulated pressure regulator valve 22771A-0K
Rear servo piston 22912A
Servo piston 22912-01K
Billet accumulator piston 22814-04K
Accumulator spring 12861-01