The 80a DE alternator has a pulley circumference of approx 210mm
The 90a VE alternator has a pulley circumference of approx 190mm.
100a RR alternator will be slightly smaller again
This will cause the belt lengths to vary a little Stock Pulley:
Alternator Belt (WITH AIRCON) : 6PK1035
Alternator Belt (WITHOUT AIRCON) :
80a Alt - 4PK0845
90a Alt - 4PK0830
100a Alt - 4PK0820
Power Steering: 4PK0845
GFB Underdrive Pulley
Alternator Belt (WITH AIRCON) : 6PK1015
Alternator Belt: (WITHOUT AIRCON) : 4PK0800
Power Steering: 4PK0845