Remember, I was first with this idea!

[jsears]

This was posted by Killcrap a while ago:

if your vin has FA91, FA92, or FA93, it is a X5ALPINA

5UXFA91XXXXXXXXXX
5UXFA92XXXXXXXXXX
5UXFA93XXXXXXXXXX

H FA91 V0103 80910000 0000000000000000 0000000000 1 N62B48 LL X5ALPINA //X5 HP LHD // Einsatz geplant 04/04
H FA91 V0903 80910000 0002000400054917 0000000001 1 N62B48 LL X5ALPINA //X5 HP LHD // Einsatz geplant 04/04
FA91 80910000 0302000400054917 0000000001 1 N62B48 LL X5ALPINA //X5 HP LHD // Einsatz 04/04 bis 09/06
H FA92 V0103 80920000 0000000000000000 0000000000 1 N62B48 RL X5ALPINA //X5 HP RHD // Einsatz geplant 04/04
H FA92 V0903 80920000 0002000400054817 0000000001 1 N62B48 RL X5ALPINA //X5 HP RHD // Einsatz geplant 04/04
FA92 80920000 0302000400054817 0000000001 1 N62B48 RL X5ALPINA //X5 HP RHD // Einsatz 04/04 bis 09/06
H FA93 V0103 80930000 0000000000000000 0000000000 1 N62B48 LL US X5ALPINA //X5 HP US // Einsatz geplant 04/04
H FA93 V0503 80930000 000A000500044907 0000000001 1 N62B48 LL US X5ALPINA //X5 HP US // Einsatz geplant 04/04
FA93 80930000 010A000500844907 0000000001 1 N62B48 LL US X5ALPINA //X5 HP US // Einsatz 04/04 bis 09/06


H FB91 V1000 81910000 0000000000000000 0000000000 1 M62B46 LL X5ALPINA //X5ALPINA 4.6 LHD
H FB91 V0602 81910000 0000000000054B17 0000000001 1 M62B46 LL X5ALPINA //X5ALPINA 4.6 LHD
FB91 81910000 0002000000054B17 0000000001 1 M62B46 LL X5ALPINA //X5ALPINA 4.6 LHD with SA226 // Einsatz 10/01 bis 09/03
H FB92 V1000 81920000 0000000000000000 0000000000 1 M62B46 RL X5ALPINA //X5ALPINA 4.6 RHD
H FB92 V0602 81920000 0000000000054A17 0000000001 1 M62B46 RL X5ALPINA //X5ALPINA 4.6 RHD
FB92 81920000 0002000000054A17 0000000001 1 M62B46 RL X5ALPINA //X5ALPINA 4.6 RHD with SA226 // Einsatz 10/01 bis 09/03
H FB93 V1000 81930000 0000000000000000 0000000000 1 M62B46 LL US X5ALPINA //X5ALPINA 4.6 US
H FB93 V1001 81930000 0000002180844B17 0000000001 1 M62B46 LL US X5ALPINA //X5ALPINA 4.6 US with Side airbag f rr compartment passengers
H FB93 V0602 81930000 0000002180844B07 0000000001 1 M62B46 LL US X5ALPINA //X5ALPINA 4.6 US without Side airbag f rr compartment passengers
FB93 81930000 0002002180844B07 0000000001 1 M62B46 LL US X5ALPINA //X5ALPINA 4.6 US with SA226 // Einsatz 10/01 bis 09/03

Additionally this information was provided from another BMW board:

The Alpine 4.6l V8 engine is Alpinas own design and porting/polishing/assembling is being done by hand at the Alpina factory in Buchloe.
The BMW engine is identical (i.e. Alpinas design) apart from it being assembled at BMW and the fact that BMW doesn't port and polish the heads, balance the combustion chambers or the crankshaft.
So the BMW engine actually has lower power output and worse efficiency than the Alpina engine. Even though the specs are identical. Shorther lifespan of the crankshaft bearings are also to be expected for the BMW engine.
But these differences are the usual differences between craftmanship and mass produced goods.

To me, since there was no official release of an Alpina E53, this is very much like putting ///M3 badges all over a 318i. Having Alpina "touch" the engine, doesn't make the X5 an Alpina X5.

But it's your car and your choice!