We've got a 5010 front end under our 4020.  It lowered the front of the tractor about 2 inches, but we'll probably never have any loader related front end problems again. 

When we had a wheel bearing go out a couple of years ago, we found out (by shear luck) that the 5010 front end has way more common bearings than the 5020, so that is something to keep in mind.  I believe the parts man said they are the same bearing used in the large frame 30's & 40's, but the 5020 bearings are just different enough that they are almost unique, and not commonly stocked.