Ok I downloaded ardunio 1.0.3 then I extracted everything in the mighty-1284p-master to ardunio-1.0.3/hardware/ .Then added the following to the boards.txt located in the ardunio-1.0.3/hardware/mighty-1284p-master.
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mighty_opt.name=Mighty 1284p 16MHz using Optiboot >> Mighty 644p 16MHz using Optiboot
mighty_opt.upload.protocol=arduino
mighty_opt.upload.maximum_size=130048 >> 63488?? with 2K bootloader
mighty_opt.upload.speed=115200
mighty_opt.bootloader.low_fuses=0xff
mighty_opt.bootloader.high_fuses=0xde
mighty_opt.bootloader.extended_fuses=0xfd
mighty_opt.bootloader.path=optiboot
mighty_opt.bootloader.file=optiboot_atmega1284p.hex
mighty_opt.bootloader.unlock_bits=0x3F
mighty_opt.bootloader.lock_bits=0x0F
mighty_opt.build.mcu=atmega1284p >> atmega644p
mighty_opt.build.f_cpu=16000000L
#mighty_opt.build.core=arduino:arduino
mighty_opt.build.core=standard
mighty_opt.build.variant=standard
However when "Mighty 1284p 16MHz using Optiboot >> Mighty 644p 16MHz using Optiboot " is selected under boards and I try and upload a sketch I get the following error:
"unknown MCU 'atmega1284p >>atmega644p' specified (then a list of at mega's)