Yes and no. The LSD would fit, but I think the gear ratios are all wrong. I'm on the hunt for a cheap MK3 LSD gearbox for this reason - by the gearbox, rip out the LSD and put it in my box - I think bulardas has already done this. Realistically though the odds of finding an LSD cheap enough make it unlikely I'll do it!
Here are the ratios. What suffix is your gearbox. I just bought one of those gearboxes from the link on this thread. It's going into a Laguna GT 4 wheel Steer (205 hp, 300Nm) The 4WS is excellent in roundabouts, can't wait to add the LSD. I didn' realise there is such a big ratio difference. I could chip it and that would cancel out a lot of the difference. I was going to do a direct swap. Now I might try to move the diff into my box to keep the same ratios. It should fit. Anyone do this before?