3 different years, same transmission, which one should I use?

For behind a small block, unless your going to be making 450 horse or more, I would stay with a 904, 727 robs horse power, I don't care what anyone else wants to say or claim, it robs horse power. There was a good article in Car Craft that discussed some of the pro's and con's of both. Here is a link 904/727 Car Craft article It certainly isn't the end all be all of info on the subject but it will give you some of the basics to help you decide for yourself.