Can not find Engine identification code

Hi, I just bought my 2003 Rav-4 and was told by the guy I bought it from that the engine had not long been replaced with a lower mielage engine, It runs really well and definately looks like its been replaced but I cant find the engine code anywhere. Could you suggest different locations of the code because I would like to confirm the engine detials etc on the vehicles V5.
Cheers