Hey Bearcamp,
As I awoke this morning a little voice in my head was saying "...extend the radius to the axle..." My visual concept of changing caster was totally wrong, and I'm sorry for confusing the issue. All points are hard points from the radius rod pivot to the axle, so the axle indeed pivots around that one, common point and caster changes are relative to a vertical line through that arc. Other than looking "different" the unequal length top/bottom rods make no difference to your setup. Listen to Jerry, Dave, Mike, Charlie, and others who know the old rules of thumb much better than I, and I'll try to stay out of the design theory questions. I hope you get it sorted out where you're happy with it, and you keep mama safe too.