well I would be very worried about the engine actually fitting in the engine bay because with the 3.5 it has now it's pretty cramped, and it's placed sideways where as the v8 in the impala is placed longways and I don't think it will fit in the malibu like that. However, if you could manage to get it to work sideways you could move as much of the stuff under the hood (the batter and such) to the trunk so you could create some space but if you don't wanna have to deal with the transmission messing up it would be best to just find a trans that can handle that kind of power because our transmissions only have 4 gears and i just don't think that's enough to handle that engine. Now as for the engine switching to 4 cylinders i think that, that would be more expensive to convert the engine to do so that to just fit in a new transmission.
And for the suspension you will probably be able to get away with the stock suspension however it would be more comfortable and more stable when taking turns and taking off from a light if you were to upgrade your springs to something stronger
Hope this helps
if you get into it keep us posted because it would be quite the interesting mod