Dodge 318
Nothing wrong with a 318 for your first swap, but as said above, make sure it's cheap. Any chance you can confirm the mileage on it? I'd look at it as a core for a rebuild since your going thru the whole swap over deal. As far as that trans, i'm not sure about the tail shaft setup from a 4wd truck to the A body? May be better off with a 904 as far as getting it mounted. Others here will know for sure. More then likely you have a 7 1/4 rear end, but if don't go overboard trying to make bigger hp from a mild 318, it should live...for a while. :)
All that said, take your time, learn what you need, and most important, enjoy the process. You can't beat the feeling of satisfaction from a job well done the first time out with the V8 power.