VA1 RBF - XF is a 3.9 for a 1600 manual tm.
VA1 REF - XJ is a 4.111 on an auto non turbo these two are stickers

T1 is a 3.9 on a 2 litre Manual non turbo
BJ is a 3.545 on a UK / Euro turbo car these three are letter stamped
BK is a 4.111 auto turbo for Australia

The VA codes are on a label [ usually fallen off ] on the diff back cover left side between the two retaining bolts vertically.

The T, B type codes are stamped on a flat vertical surface on the right side of the rear diff in the angle where it changes from the nose of the diff to the main case.

OR T1, BJ, BK, can be stencilled in in white paint on the top of the diff

Според този код дифа е с предавателно число 3.9