yes indeed. it will be a mix of Fiat, Suzuki, and Bmw

(and possibly an MOT and insurance nightmare. standard issue with me.)
i have seen it done with a seat marbella. i think you will need to weld in supports for the front of the rear leaf springs. you may be able to adapt the original 2wd mounts however. i think you would need to change what angle they are as they point inward to the middle of the rear bumper. if you cut them off, welded in some strengthening then welded them back on or just made new mounts (lets face it they are only leaf springs). the rear mounting points of the leaf springs just needs a hole drilling out through the rear structure behind the rear wheel and a metal tube welding through. i dont know if i have any photos on my
>> project fallout thread << as that was pretty rusty (but not as rusty as the 4x4 i have just bought)
for the middle, you will have to take the prop shaft and weld in some captive nuts or studs to mount it to.
you will sadly have to get rid of the 2wd plastic fuel tank as the prop shaft would go through it. sadly 4x4 fuel tanks are really expensive now days. so a tank in the boot may be your best bet. less you can weld 2x jerry cans together (to make them wider) and fit them on the filler side of the car.
the hand brake cable and brake flexi to the rear axle are supported via a bracket on the fuel tank.
the 4x4 handle could be made to fit by just using bolts through the car floor. i am not sure what you have but i have never seen a 4x4 fiat panda with cable gear linkage, only rod style. my guess is they have them in europe on cars newer than 1995 when they stopped coming over to the uk.
other than that, you dont really have much else besides the sump guard and 4x4 engagement indicator light on the dash. #
i wish you the best of luck...
... you can weld right?