PARTS:

R1   330 ohms
R2   270
R3   470
R4   1.5K
R5   1.2K
R6   100
P     100 ohm pot
C1, C2, C3     100nF ceramic
Q1,Q2      BC327
Q3     BD244A
D1     1N4148
D2      BZX6V2 zener, 6.2V
D3      1N4003
D4       has no markings, but a 10A, 50V diode should be OK.

D+   Regulator input, from output of diode board and to alternator telltale lamp.

Df    Goes to one brush/slip ring of the alternator rotor.

D-    Goes to the other brush/slip ring of the alternator rotor, and to bike ground via a brown wire.