Sure, the 324 is in the '1284 'family'.
Set up your IDE with maniacbugs '1284 cores
and copy the 1284 stuff into a '324 section, modifying the signature bytes:
Part Signature Bytes Address
0x000 0x001 0x002
ATmega164A 0x1E 0x94 0x0F
ATmega164PA 0x1E 0x94 0x0A
ATmega324A 0x1E 0x95 0x15
ATmega324PA 0x1E 0x95 0x11
ATmega644A 0x1E 0x96 0x09
ATmega644PA 0x1E 0x96 0x0A
ATmega1284 0x1E 0x97 0x06
ATmega1284P 0x1E 0x97 0x05
I'd give you better direction, but I haven't looked at it in a while, and it's late here ...