Could your switch body be reversed from stock? My 1980 is aligned as described (I probably have that spec sheet in a file somewhere). I'll do some tap-checking on mine to see but I suspect you're right - boost is likely not single coil.
Another update on the L-1000. In single coil mode, it's the coil closest to the bridge which is on (misremembered that one). In OMG mode, which I take to be series, the coil closest to the nut has the capacitor and sounds much bassier than the coil closest to the bridge--based on best tapping with a jeweler's screwdriver.