Sid, 2 way?

Disc type, like ZF. Though, if people want, they can be Torsen type too. Torsen is somehow even better. It will adjust the power to the tire having more grip. Though, if the other is completelly in the air it dont have torque enough to do a thing...
If Im correct there are two different differentials in 131. Early version (Mk1-Mk2 cars?) 22 splines in halfshaft. The Mk3 had 24 splines and this wont fit them. BUT, only way to be sure is to take one half shaft from the car and calculate the splines.
If there are interested enough for 24 spline version, it can most propably be done too.