Do you speak Russian by any coincidence? You could ask the Russian forum, they sure do need all the ground clearance they can with their roads :
http://transit-club.com/forum/15
You will very likely raise your van due to the Kilen springs (22/145/275 mm) being new, but so will the standard ones. If you could find a version declared as e.g. 22/145/285 mm, I would ask them to guarantee the dimensions before ordering. 10 mm difference should give some 15 mm of lift.
Please forget my suggestion about spacers on the strut bearing, I forgot the Transit has springs and dampers separated. However, the same principle can also be applied on the spring. You could take the aforementioned Coil Spring gap Assisters Spacers and place them ON TOP of your springs, not between the coils (where the amount of lift will be very small). You will have to mod the upper side of the spacers though. 20 mm spacer should give some 30 mm of lift.
In the same way, one could use a spacer UNDER your springs (on the wishbone), like the lift kits for the 4X4's do, for example:
http://www.ebay.de/itm/Federteller-Set- ... 0005.m1851
or just use a spring isolator instead as a spacer:
http://www.ebay.de/itm/Federteller-Fede ... xyeZNTRsjn
In both occasions, finding one that fits on your wishbone & spring will be the hard part to find out.
If you want to go Russian, or African, you might just take out the spring isolator, fill the gap between isolator and bodywork with polyurethane/MS-Hybrid putty, put the isolator back in, and let it cure for a week. Does not cost a lot and will be virtually undetectable. German vehicle inspection would burn me for suggesting this, as would a lot of Germans themselves, but it might very well work. Only reason it might not would be the cured putty layer not standing the pressure, in which case the front would sag again, but one can raise the hardness by mixing sand into the putty. To explain, look here:
http://www.fordcat.ru/shop/1/parts/17661 (Between part 11 and the bodywork cup)
As you can see, a lot of options. Good luck.
Ciao, Kai