This is from Club S12 where GerryB did a short write up on what it took to get his S13 VLSD to work in the S12... which I'll be doing in the next 6 months.
I have an s13 VLSD centre in my longnose s12 type 4.11 R200. It bolted in fine after I swapped the s12 crownwheel on to it.
BUT for the RHS drive shaft I had to take the inner CV off and swap the s13 inner CV on to it and run the s13 RHS input shaft in the diff to operate the Viscous centre. Also had to cut off about 8mm off the end of the spline that goes into the diff of the LHS s12 driveshaft, so it didn't fowl on the viscous coupling.
After these mods was just a bolt up.
(I got the VLSD reshimmed also before fitting it, (extra shims) to make it real tight.)
http://www.club-s12.org/forums/index...howtopic=16318