Looks like they are in:
/mighty-1284p/bootloaders/standard/ATmegaBOOT.c
Need to get someone more knowledgable to figure out what to do with that file once its modified.
Or maybe it doesn't need modifying?
This looks close
#elif defined AVR_ATmega32
#define SIG2 0x95
#define SIG3 0x02
#define PAGE_SIZE 0x40U //64 words
Probably have to make a new entry under boards.txt as well.