This should be a simple one if you know the answer...does the Manitou Swinger Air 4-Way SPV shock have to be installed a certain way up; .i.e reservoir down?
Good shocks, but be very careful to make sure you never run with less than 50psi in the SPV chamber, you can screw the shock up if you do. And you will have to check it every week or so.
I have a Fox one that seems to be fine, its better for higher pressures, as some have gauges that don't go too high. Check what sort of range you need one to go to & get stuck in.