I have the exact same gear shifters. I am currently trying to rebuild the left hand one but I'll try help you with the right hand one.
1. Washer G would go in between the two moving arms.
2. I reckon you have to place both bits in the top of the gear shifter and then tension the spring afterwards by pulling it across with a flat head screw driver.
I am stuck with assembling the left hand gear shifter. I have put it all back together except I can't work out how the spring on the underside goes back in. It just seems impossible to put that spring back in. Anyone know how to fit the underneath spring?