It can be done, no issues if you have right tools and skill set.

Buddy of mine used my old '08 4.8 exhaust on his '08 3.0si, when his exhaust rusted out and got a hole in it...

As stated above he had to weld in a Y pipe.

It's working fine.

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2008 4.8i X5 (2/25/08) 105k:
Titanium Silver/Black; All -HUD; Aero Kit; 22" VS-130 w/Pirellis;
///M Shifter & Fr Brakes; Gauge Rings; Console Pads; Custom Wheel & Mats; Roof Rails
Carbon Fiber: Int Trim, Nav Surround, Grill, Cluster Trim, Shifter & Eyelids
1.2" H&R; LUX AEs; LCI Tails; Rear Fogs; NBT EVO; ESS Tune; Meisterchaft GTC Exhaust