Hi DARE U, I cannot confirm it that is 20mm front or 40mm rear, because every wide body kit may be different and it is also to your own liking on how width your wheels want to go. I have seen some are as wide as 50mm for the rear fitted with Lumma wide body kit. The best advise for you is to get the wide body package from Lumma and it does include the wheel spacer.
But just before you purchase please check with your insurance company if they will still insure your car if fitted with wheel spacer.
Here are some picture of my H&R hub centric wheel spacer for my X6, due to the insurance regulation of wheel spacer fitted in cars in Australia, I have not fitted them in yet.
