iMac 21.5-Inch Late 2015
To open the Mac you cut the tape holding the screen down as Apple decided to glue the screen in...
The ROM is a WSON-8 chip 5x6mm (64Mbit MX25L6473E).
The ROM in on the top (easy to reach) side of the motherboard.
The SPI connector is a Hirose-12 but is not mounted by Apple.
The board number is on the top right corner of the board.