Sounds like you created a new folder under the hardware folder to contain your new boards.txt file. In order for the compiler to find the right arduino_pins.h header is for the build.variant line to look like this:
atmega328bb.build.variant=arduino:standard
By the way, that baud rate has to match the baud used by the ArduinoISP sketch (mine came set to 19200). Trying high baud rates created new problems with data overruns. You might also want to find your programmers.txt file and set the baud for ArduinoISP there too.
Here is the whole board description for my mega328p running at 20MHz on a breadboard:
MWB20MHz.name=ATmega328 on a breadboard (20 MHz external clock)
### MWB20MHz.upload.protocol=stk500v1 # commented to allow the upload.using line to work right
MWB20MHz.upload.maximum_size=32256
MWB20MHz.upload.speed=19200
MWB20MHz.upload.using=arduino:arduinoisp
MWB20MHz.bootloader.low_fuses=0xF7
MWB20MHz.bootloader.high_fuses=0xDE
MWB20MHz.bootloader.extended_fuses=0x05
MWB20MHz.bootloader.path=arduino:optiboot
MWB20MHz.bootloader.file=optiboot_atmega328__20MHz.hex
MWB20MHz.bootloader.unlock_bits=0x3F
MWB20MHz.bootloader.lock_bits=0x0F
MWB20MHz.build.mcu=atmega328p
MWB20MHz.build.f_cpu=20000000L
MWB20MHz.build.core=arduino:arduino
MWB20MHz.build.variant=arduino:standard