1. - The External Memory Bus is not implemented on 64-pin devices.
The 18F67K22 is a 64-pin device.

2. - The External Memory Bus extends the "Program Memory" space.
It does not extend the GPR (General Purpose RAM) space. So you cannot put PBP variables in that area.
But, you can use READCODE and WRITECODE to use that memory for data storage.
Although, you would need to use an 80-pin device, and compile with PBPL.

3. - PBP will not work with the "Extended Instruction Set" (XINST) enabled.
But the Extended Instructions have nothing to do with the External Memory Bus.
XINST affects FSR2, the Access Bank, and software stacks used by the C language.