Thanks Al! That little bit of pertinent info is well hidden in the data sheet. The I/O section doesn't even mention this limitaton for pin PortA.6. Since my device has this pin I guess item 5: as you listed applies in my case.
Now I have to figure out how to set Oscillator ECIO or RCIO mode. I'm now trying to figure out how to set the configs to do this for the 18F452.