I would like to know the height and distance of the rear axle relative to the BB center in a coordinate system where the frame is rotated so that the head tube is perpendicular to the ground. I think this is JFX and JFY. Can you confirm?
Bicycle Design Software
You are correct. These dimensions were setup for a builder who had made his own fixture which held the head tube vertical and had mounts positioned along a baseplate for securing the bottom bracket shell, seat tube and dropouts. This is similar to another set of dimensions created for DEAN bikes. The fixture at DEAN holds the seat tube vertical rather than the head tube.