[Fredrik Emilsson]

501X had 16T center and 36T rear diff pulley and 35T front (black one).
363 mm belts.
The 36T pulley does´nt have openings (like the 37T has) and uses 8 diff balls.
36T pulley:


37T pulley:



501X WE had 18T center and 37T pulleys.
12 diff balls
369 mm belts.

511 had 18T center and 37T pulleys.
12 diff balls
369 mm reinforced belts.

Also agree with Jan and Johannes. The reinforced belts lasts forever. Never had to adjust tension.