I did the swap with basic air tools and a floor jack. It's really not the hard to do. I think it took about 45 min but I've had my jeep apart so many times it's second nature now. How tall is that rear poly spacer? Back when I had the BDS lift years ago their rear spacer was approx. an inch an a half tall so when you install the lift the XK sits level. If your rear poly spacer is an inch and a half then the rear of your XK will sit a little higher with the OME springs. Also with the OME HD springs you won't get sagging in the rear while towing due to the higher spring rate. I would remove the poly spacer.
As for the bump stop spacers use 2 inch tall by 3 inch wide performance accessories body lift spacers. They work perfect. I get mine from the local off road shop. You can find them on summit racing I believe and they are cheap.
As for the shocks, anything two inches longer than stock will work fine.