My lovely E38 needs more power :)

Hello guys,
I have a 728i '97 E38 automatic gearbox.
I realy love my car and I think I will never ever sell it.
Never ever?
Yes!Never,ever eeever
It has all I need except the power.
Now it would be easier to bye a 750iL but I just love the one I have and it won't be the same.
So what I am thinking is (and you will tell me if it's possible) :
I want to swap the 2.8 I6 engine with the 5.4 V12 (M52 with M73) and then take it to ac schnitzer for the tune-up.
Am I crazy or it's doable?And if it is what else do I have to change (ECU,gearbox..)
If it's not possible with the M73 I guess the M62 4.4 V8 will be good also.
Thank you very much in advance :P

Sorry for the double post,i got the wrong section
The original thread is in 7 & 8 Series.