They make a variety of stems.. I think on the one I did I machined part of the top threads off and moved the bearing area back higher up with a split bushing.... The bearng tapped on nicely.!! Ah..nirvana.. I think it was a 450 stem which is shorter between bearings than the 750. Will try to add a diagram
The split bushing is sized to fit on the machined step in the stem. The OD and ID must be precise to get a no slop fit, and the stem must be at very little or no run out to insure concentricity. Not sure what we did at the top tree, but one trick to use is a bushing if stem is too small, and thread internally for bolt if stem is too short.
Hope that makes sense, some will get it.