My Dodge Sprinter 3500 was recently converted (almost) to 4x4.  Dodge puts a German made Werk Kassel 4.18 ring and pinion in the rear.

The conversion company did not realize the rear was a 4.18 until they had already installed a Dana 60 4.10 up front.

Any one having information on the easiest, most cost effective method of converting the Dana 60 4.10 to a 4.18 ring and pinion would be greatly appreciated.

Thanks!
Frustrated  

You are not going to find a 4.18 anywhere for a D60 so do not waste time looking. I do not think that the 1% difference is going to really be a issue for you as you can get that much difference on matching axle ratios and different tire pressures and loads.  

Good luck on that one. You will notice the rear gear being a little slower or a dragging effect. But can b corrected slightly with air pressure. Shouldn't be a big issue. used to run a 4.09 frt/4.10 rear on another truck. I now run 4.10 frt/rear and keep front aired up a little more than rear on highway travel. One other thing is find some soft dirt and drive in 4wd and look at your tire tracks If you tire pattern is nice and smooth with front and rear when traveling straight its not an issue. but if tracks are dragging or pushing the dirt you have a issue when traveling in a straight line. Cheap little experiment to check out. Scary simple. I do this check when playing with air pressure on ice with my studded tires, 40" hawgs. O'yeah travel forwards and then backward and see what happens interesting little test.