I've uploaded a screenshot of my cad design to try and portray a better of idea what we're doing. The spindle will be mounted somehow statically to the two plates, allowing the attached cranks to spin freely.
In the design, the spindle is floating, unattached to the plates, due to the fact that I don't know exactly how they work. Hubs often have mounting hole patterns. Do spindles have these as well?

http://www.ufhps.org/drivetrain.jpg