Dunfield has its AppNotes under free downloads.

APN5101.DDS tells how to create new sfr definitions.

asm {                           ; Begin inline assembly
    MCON EQU   $C6              ; Memory Control register address
    TA   EQU   $C7              ; Timed Access register address
}                               ; End inline assembly
extern register char MCON, TA;  ; 'C' definitions

What I still miss is the predefined macro to identify Dunfield and I would very much like to know if the asm also accepts 0xC6 instead of $C6. If not it might become very hard if not impossible to support it.