I would go with a 440. there isn't that much of a difference in size. I think the width difference is 3/4 of an inch than a 383. I could be wrong. personally I don't like fenderwells, and it doesn't sound like you are wanting to cut up your car. a cheaper header would be out of an E body. I am pretty sure that is what I have in my car. ( headers came with car, and I couldn't find a part #) I did put it together, and the headers need just some slight mods to fit. E body headers start at $150, and I think underchassi BB headers start at $600, so there is a big difference in price.
The Automatic tail shaft is longer, so you will need to get your drive shaft cut and shortend and balanced. Should cost about $100
I agree, don't change the K fram. it is just fine.
I would recomend an aluminum Rad. should be able to get one for $300 or so.
and I also recomend frame conectors. lots of people say you don't need them, but I would rather have the extra streigth, than to find that my doors don't close properly, and put them in later.
Its expensive, but have you considered 4 spd. I love it.
The reason I say BB, istead of SB, is cause you get noticed more. Lots of 340's and built small blocks at car shows, but they don't get looked at like a BB A body!!!!!
Phil