Hi bitcurrent
You are right, the green big thingy is R2; this is a 0.47R 8W shunt resistor (SETA RB60)
Only one OpAmp is required for this project.
LM324 is a Quad OpAmp, LM358 is a dual OpAmp, both are inexpensive and OK for the job.
I finally switched to LM358 (8 pins) to save room on the PCB
The top side looks nice
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1266140108
The other side is... a bit more cluttered 
Adafruit shield is V.5 as per Adafruit Proto Shield for Arduino Kit [v.5] : ID 51 : $15.00 : Adafruit Industries, Unique & fun DIY electronics and kits
My advices:
First build your prototype on a breadboard Half Sized Premium Breadboard - 400 Tie Points : ID 64 : $4.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Install only basic parts, ignore relay, buzzer and voltage divider
You don't need the heatsink if you only want to test AA or AAA batteries
Make sure everything is OK before any soldering
Develop a simple software that displays Volts and Amps on your computer.
It will be easy to add features once you have the basic design right
Oh... I finally built vesion 1 circuit, please ignore V2
Good luck,this is a very educational project