Chris, I think you are using needle bearings at the rear of the lower link instead of the bigger bearings. What is the bearing ID? I don't have a set of girdraulics to look at now, but I am not sure a new lower stem would be necessary to switch to bearings. A new smaller concentric part would be required to use the original FF2 spindle if the standard eccentric OD and the associated pieces could not be reduced to that ID. Probably not worth the effort except as an expensive experiment to determine the way friction affects the forks, since such brilliant solution has already shown so much success and has been made available and tested by some really generous and dedicated people. If one was to go to all that trouble, we might have to start a new never ending topic on the forum, and I'm sure we would rather be riding. The experiment would also violate the one change at a time method since the eccentrics are changed.
For Bill, I know you are aware that the center of the eye of the lower link is midway between the solo and side car position, so a concentric would not have that great of an effect on trail. The pivot would be only 3/16" different, not 3/8" like the sidecar setting. Davidd used a concentric on his racer without any concern about reduced trail, but given your past experience, I understand the misgivings.