I am told the main difference is the engine sump which is a bolt on change over - Don't quote me - examin the engines.

you can put a viper v10 in there if you wanted. just takes time and some modification

You will have to do fabrication, and spend a decent amount of money. Can it be done? Sure just have to ask yourself how much are you willing to spend on an iX.

your best bet and basically only option is to buy an E34 525iX as you will need the M50 sump with the front diff etc. you will then need to modify the E30 subfram to accept the engine as the bottom of the sump is lower to accomodate the diff. if your lucky the geometry of the front axels will line up otherwise your screwed.

all in all, some projects not worth tackling, this one might be a bit far. get an E34 525iX and put your S50 in that instead.