Yes
the diffs are interchangeable,
the shocks do fit although the sp1's rears are longer, (That is no problem)
I wouldn't say the same for the lower arms. They are indeed different both front and rear, but I have never tried putting them on. One thing is certain, if you use the Kanai2,3 arms on an SP1 or the opposite, you 'll have to check the car on a set up board, once I dont think that the corresponding let's say 3 degree toe in rear plate will give you 3 degrees of toe-in. (If you understand what I mean, I cant really explain, but I guess you get the idea)
Front knuckles
Fuel Tank
Engine bases
Radio box (duh!!!)
rear wing post
brake assembly
center diff assembly
Sway bars
are the same for all cars.
Hope this helps a bit
Antonis