Is there any advantage or disadvantage, to a leading swingarm, other than bearing hub not being above or below frame rails? 
I built my own first leading swing arm and noticed immediately that it absorbed harsh bumps musc better than any other type I have had. ( I have had ten sidecar rigs now).
I believe this is when a trailing arm type encounters a square cornered chuck hole, It imparts a rearward shock before the wheel begins to rise. This action is far less noticeable with a leading swingarm. Also the direction of movement of the suspension is in a more or less straight line with the lenght of the shock absorber.
There are probably engineering types on this site who can speak of this with better definition but these are my perceptions with actual over the road expirience.
Phelonius
I'm in the process of building my first sidecar and rig and am planing to haul my wife sitting in her wheelchair and also change car to something more conventional and liked the idea of the pivot being in the same plane as the top of frame rails. My swing arm uses trailer axle stubs on each end mounted in 1"x4" bar stock with a frame of 1 1/2" square tube .120 wall. The bike is a'76 Moto Guzzi Convert.
Sound like avery substantial rig.
Phelonius
