Look at it this way Teej, wouldn't you hiss and strike after you'd been neglected, hurt, left to go hungry and thirsty? I know I sure would so it's pretty much completely understandable for any creature to act this way after mistreatment over the long term. In other words, in my mind that snake's doing exactly what I'd expect it to do.

I'd suggest as well to make sure your husbandry is bang on, put the snake's setup in the quiestest place in your home, add in crumpled newspapers and just let it be except for feeding, watering and general cleanup. After a couple of weeks or so, try just gently and quietly reaching in to stroke it down the second half of it's body if it will allow that so it gets to know your smell and that this means it's about to be picked up. Pick up gently but firmly, don't show fear, wear gloves if you wish and just hold the snake for a few moments. Don't have anymore people near the snake than you have to. Try hard to make sure removing and returning the snake are not times of high stress so it can learn the routine of gentle removal and return to it's home.

Try to handle in the evening when the snake is awake. Avoid handling when it's hungry or for 48 hours after it eats. Take your time and respect the snake's limits. A couple of short handling sessions per week may be all that it can accept (short as in 10 minutes or less). Some will come along and accept handling but remember handling is a joy for you, NOT a necessity for your snake so be glad of what the snake can give you that way. Some will accept handling, some won't...some will improve that way with time.

Part of taking in neglected creatures of any species is knowing that there must be tons of time and patience and that your goal may not be reachable any time soon (if ever). Best of luck with this snake. If you search the word "brannagh" you'll find tons of threads about that big female and the time we had getting her safe to handle. Now she can be handled by 5 year old children (under supervision of course). Just because that worked with Brannagh though doesn't mean it will with every snake....they are wonderfully unique creatures.