Hi xl97,
even it's off-topic, one of my next project I am working on is an special Arduino board with library for very low power applications. I already got my own bootloader for mega328 with 8 MHz internal clock (but 32kHz crystal-calibration) to work - I placed a boards.txt in a folder under /hardware/<my_arduino_board_name>. Compared to your file, it contains two lines that seems to be important for compilation:
gcduino168.build.core=arduino:arduino
gcduino168.build.variant=arduino:standard
Maybe that info will help you...