Custom Rabbit 2000

I am using Rabbit 2000 series. I know there is board type RCM 2250 with 2X256 flash. Can I use 512K flash as primary. If so what board type do I define in ID block? Since there is no 512K primary flash rabbit 2000 board type defined in boardtypes.lib.

If I define my custom board type, it does not recognised realtek ethernet. Basically if some one could throw me some light on which files I need to edit for my board type, that would be very helpful. (Rabbit 2000 512K flash primary 512K Ram and ethernet)