3S-GTE JDM 2nd Gen Turbo Engine USDM, Gen2, and Gen3 identification

3S-GTE JDM 2nd Gen Turbo Engine, guess, attach, http://www.caburian.com/web/wp-content/uploads/2013/09/image3.jpeg, link, direct, pics, gen3, gen2, identification, reason, usdm

can anyone lead me to the right direction identifying which gen motor I have acquired, im having the motor rebuilt but the valve spring retainers have shim over bucket for gen2 and him under bucket for gen3 problem is.. i don