I have done some communicating with Whitefeather. They can modify a 2WD Sprinter into 4WD. Their lift is slightly higher than the stock 4x4 Sprinter. Also, they can put a differential lock on the front axle. SMB is not allowed to do this. No lock can be put on the rear axle of the stock 2WD or the stock 4WD. They also widen the axle and claim better MPG on their conversion.
Here is what they told me:
Thank you for your request for information.
The Sprinter, like all motor vehicles is a tool. Which tool is right for you depends on what you want the tool to do and how long you want the tool to last. The factory AWD/4x4 Sprinter is by their own advertising and videos is for limited traction conditions on road, mostly snow and ice. I also understand from owners it goes back to 4x2 at 50 MPH and gets lousy mileage. There is a large market for on highway traction.
Our 4x4 which we have been building since 2007 is comfortable at 80 MPH on highway but has been inspected, tested and approved by the U.S Army Proving Grounds Aberdeen on the off road tank track. The Sprinter rear axle has an electronic traction control, the ring gear is welded to the carrier so it can not be changed. We do offer a selection of front axle traction options, ARB, OX Lock, and the TruTrack ( our most popular option ). The factory AWD can not be turned into an ambulance in North America, it does not meet stability stds. Ours does. On winding roads ours is comfortable at approx. 15 to 20% higher cornering speeds.
In our 4x4 conversion we widen the Sprinter rear axle by 5 inches, and our front axle is 4 inches wider than the stock Sprinter plus we install better front and rear shock absorbers and front sway bar to control body sway on corners and high wind. You have to be able to drive when the wind blows.
The factory AWD Sprinter is lifted 4.5 inches but Mercedes does not widen the axles or improve sway bars or shock absorbers so theirs is just less stable.
We start with Goodyear Adventure A/T Kevlar tires but offer many other tire choices to make the tool fit your needs. We also have our own line of aluminum front and rear bumpers, nerf bars /side steps etc. to make your tool right for you.
Please let me know if you need more information.