E39 M5 Touring query

All,

I have recently settled on a E39 540i touring as the closest I can get to a
fast estate within my current budget ... I'd have gone for a 2000ish M5 but
I really do need an estate and cannot afford the new one yet ...

An idle thought but ... how easy would an M5 lump slip into a 540i? Are
there any big powertrain differences to deal with (g/box, axle?) and I
wonder how tricky the electronics would be ... ?

I've already got used to the 540's rapidity and I reckon doing a conversion
might still be cheaper than an RS6 Avant!

atb

Steve