OME is longer. I think they are something from 1/2" to 1-1/2" longer (there 4 different types of springs for different loads), but they are also a different rate springs.
I think if you want just to add springs, try OME 883 for the front and OME 895 for the rear. But you should remember that you'll be very limited to the down travel.
The spacer technology use 2 spacers on front strut: preloading which sits between spring and top plate and lowering which positioned on top of the top plate. First preload the spring and virtually make it longer, the second one is lowering the strut itself down. With OME 883 you will extend the stock shock, so you wouldn't have much down travel.