You need equal length driveshafts. With factory LSD the gearbox housing is different and extends into the middle of the car. Thus the need for equal length driveshafts.
yes, factory LSD is inside the box. aftermarket LSD is fitted outside the box. so if driveshafts are not equal in length then you dont have LSD fitted. according to what you say both driveshafts are same length if its LSD. be it aftermarket or original since original LSD housing extends onto right to middle of car.
so..
stock or aftermarket LSD = same driveshaft length
No LSD = unequal driveshaft length.
Am i right ppl? damn this thing gets confusing the more you try to understand it