If you've got to split the box to drop the 4.11 diff (that's what you're running now isn't it??) in, you might as well go the whole hog and throw the L series low range in there too

There are threads about how to do it on here, I remember PeeJay wrote up a good one to do with his forester gearbox, there was a bit in there about some input shaft thing that needed to be modified too, I don't know if this will be applicable to what your gearbox needs but it's good to read up on it anyway.
You'll also have to shave the Ring gear so it clears the low range gearing

Cheers
Bennie