go with the same model year engine weather you go small or big block stick with the same year, you will have way less problems with the computer and i dont know if you have emissions tezting in your area but that will play a huge part in the regulations , but the job is fairly easy if you have mechanical knowledge or are pretty handy with your hands and working on cars, you will have to change over the computer and harness and it will probably be a good idea to switch the trans as well you might think that everything is the same but believe it or not it is not, i wanted to do the same thing with and i know alot of the techs at the local dealer and i'm pretty sure the trans tech there said that the tail shaft is smaller in the v-6 than in the v-8 also the rear end is different but they said that the rear should hold up unless you were planing to go like to 500HP or something then you will have problems nut anyway any questions you have go to your local dealer and ask the techs anything you need to know, if you just walk into the shop area you should find their head tech and the trans tech those two guys should be able to answer any questions that your wondering about.good luck ,buddy!