avr_fred:
Use the Duemilanove board type in the IDE as it used the non-p version of the chip. Other than the lower power and the different signature, they’re the same device.
The board definition for Duemilanove specifies ATmega328P:
diecimila.menu.cpu.atmega328.build.mcu=atmega328p
That will cause the signature verification to fail if you try to burn the bootloader to an ATmega328 with the Arduino Duemilanove or Diecimila board selected.
MiniCore has a board definition for ATmega328:
- Tools > Board > ATmega328
- Tools > Variant > 328 / 328A