Multiplexed AMS3-2 lines in BF514


In our design using the BF514F we would like to use VDDMEM=1.8V and VDDEXT=2.5V and all the async memory banks. The datasheet for the BF514 states that

When using any of the asynchronous memory signals AMS3–2, ARDY, or AOE VDDMEM and VDDEXT must be shorted externally because these signals are multiplexed with GPIO

Is this due to internal circuitry in the BF514F or will it work to add an external level shifter on the AMS3-2 lines?