ok so i have two diff here one from my s80 ls tranny an another from what the seller so called a ys1 with LSD. now the question is both final gears have 64 teeth the s80 has 2 notches on the ends of the teeth but the lsd doesn't have any notches. so could i put the lsd an the final drive in my tranny? (of course with a lil grinding on the case)

 

Switch the FD gears and yes you can put the LSD in. If you keep it the origanal way and just switch them it will not work. And the only way for a YS1 to have LSD is to have come from japan