I used to encounter a lot of people who would tell me "to make some real power" I should "drop a supra engine in" to my (400+bhp) MR2 turbo. The supra is front, longitudinally mounted, engined, rear wheel drive inline six cylinder, the MR2 is a transverse mounted 4 cylinder, the gap between the brake disks on a MR2 is about the length of a Supra engine. your idea of putting a BMW box into a freelander is similarly incompatible with reality.
However, as you say, "there is a way of doing it", and you are fortunate enough to be talking to someone who can engineer the frack out of stuff, but this gearbox conversion is not an easy weekend project. If you simply must make the hippo use an 320d gearbox, you'd need to do some
SIGNIFICANT changes to the vehicle, like rotate the engine to make it longitudinally mounted like a Discovery / Range Rover / Defender, then you could use a custom prop to make the vehicle rear wheel drive. If you wanted to keep the hippo 4wd, you'd have to use something like a BMW X-Drive gearbox which has a central tailshaft output that could drive the rear diff, then put a separate rear diff in the front axle with custom driveshafts.
OR, if you wanted a six peed gearbox, but weren't too fussed where it came from, you could look at other transverse mounted 4wd vehicles as donors for complete running gear transplants, such as a Mitsubishi EVO, or an Audi TT or A3 Quattro, Toyota Celica GT4, Caldina, Nissan Sunny GTiR (Pulsar). Someone did a Subaru engine conversion into a freelander, video is somewhere on here, but I am uncertain was it AWD or FWD.
How good are you with a computer and how serious are you? If you are half competent with a computer, like can make a powerpoint presentation, and are serious about doing this, you could start to mock up block diagrams using these pictures as your templates.