Well, I fitted a S1 transfer to my S3 box and the 2.89 ratio VS 2.35 rings a bell.
This is about 23% lower, only in low range.
The idea of fitting some other gears to the existing case doesnot work I think, because the intermediate shaft is smaller in dia, and the casing has smaller holes in it.
I believe that you cannot have the lower range with the bigger intermediate shaft, because the smaller gear wouldnot fit.
Anyway, the endresult was very good for me, with a 100Hp petrol engine it was reliable for years.
Daan