Ramp is pretty much done now, except for a few more details. What I ended up doing was to make a "cradle" for this section to rest in while I got all of the angles, etc. worked out, as well as a temporary guide on the upper portion to make sure the pistons stayed plumb while the ramp was being raised or lowered. Everything is just dry-fit for now, with brad nails serving as hinge pins for the bottom of the ramp pistons.
ramp separated, showing the hinges:
closed position, held in place by magnets
As always, comments/critiques welcome!