Well you want a different motor AND a different sunroof setup so that's body and motor. Better to buy a different X5. If you wanted one or the other especially if it was just motor then it might make sense but cost wise to do the mods your talking about would cover the cost of buying 2 X5's.

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Just BMW's - All cars and trucks was two pages long
1994 318is
1997 528i
2000 323i
2001 X5 3.0 auto
2005 X5 3.0 auto
2011 535xi auto
2013 X5 xdrive35 Turbo
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Aftermarket E53 Radio Install