First & foremost, make sure you eliminate/resolve any physical issues he might have, such as back, saddle, teeth, other tack, etc. These issues are often pain related.
Unfortunately, if you rule out pain, and he was as good as you say when you got him, it sounds like his problems may be with you or the situation he finds himself in now(sounds like others deal with him too?). A *good* instructor/trainer might be a great help to work with you & the horse, to ensure you're going about things in the right way. Diet & management could also play a part in his behaviour.
While you can(usually - some won't tolerate it, end up 'rogues', 'untrainable'...) just make the horse to just do what you want, I believe that the horse's attitude is just as important as the behaviour he gives me and I want my horses to enjoy my company & games too. My horse is recreation for me & I want me to be so for him too.
Specifically to your questions...
"Now, he fights me to get on. I will even just stand and hold the stirrup, and he'll try to swing his head over mine to back up. I have tried sharply scolding him to stand and not move, and he will stand for a few seconds before moving around again."
He obviously doesn't enjoy being ridden any more for some reason and seems rather 'vocal' about it. I personally wouldn't ride a horse like that, until I'd taught him to be comfortable with me mounting. Scolding him & making the situation more unpleasant is not likely to improve his attitude - just means he's ****ed if he does(you get on), ****ed if he doesn't. I would be breaking the task of mounting down into easy steps and rewarding him(with something Good, as well as removal of Bad, ie. Your pressure to mount) when you get the 'Right' behaviour, no matter how small that might be to begin with.
Eg. What do you do when he stands for those few seconds? That is the behaviour & instant you need to reinforce to begin with, not punish by putting more pressure on him in continuing to mount. "Well standing made matters worse so I'd better try dancing around more"
So... I'm holding the stirrup & my horse is moving around, telling me he's not happy about it. I keep holding the stirrup(keep the pressure on) if he's not too upset by it, with the rein shortish but not tight, just moving around with him. The instant he stops, or even hesitates to begin with, I let go of the stirrup(negatively reinforce, remove pressure), say 'stand' and give him a scratch or a treat(positively reinforce, reward). I repeat this until he's obviously comfortable standing while I fuss around before I ask for a *little* more & repeat the process. In this way, using 'approach & retreat' tactics, you can get a horse confident & comfortable about just about anything that doesn't hurt him.
Unfortunately there is no shortcut to repetition in training, often especially in 'retraining', due to the horse's possible opposing experiences. To begin with this process can be slow, depending on the horse's previous experiences & understanding. But the more you approach things in this way, the quicker it gets and the more it rubs off on everything else you do with the horse. That is one part of what I think of as real respect - it can be earned when I am respectFUL of the horse.
"2. Lunging: Murray use to lunge really nice, with and without tack. Now, he rears, and cowkicks."
This sounds like he's 'giving you the finger', telling you you don't have the right to ask him to do that. He sounds possibly a rather 'dominant' & smart personality. I would get after that behaviour, make it known that this is not tolerated, but I would also make a point of making things worth his while. Encourage him to want to do what you ask, so you avoid many battles in the first place. Again, breaking things down into easy steps & practicing & positively reinforcing these before asking for a bit more is a big key.
I think you need to make a point of being just(I'm sure you do at least some of the time) nice & fun to be with. Initially I would avoid doing anything unpleasant with him for the time being. Spend lots of time just hanging out, brushing or scratching him(if he enjoys that), feeding him, etc.
'Catch' him to do this, then let him go. But again, if that's too much for him right now, break it down & start with, say, giving him a treat for allowing you to approach him. This can gradually progress to touching/rubbing him with a halter & then putting it on, taking him out, etc. Even once he's again good at coming when called, make a point of only doing nice stuff to him for the first few minutes at least, and work on getting him happier about the stuff he finds hard about life with you now.
"-hasn't done "work" in about a year. Just lazy riding from the last owner."
While you may see what you want of him as 'work', if you want him to perform for you with a good attitude, I believe you have to make what you want 'play' for him, or if not, at least rewarding & worth his while. I would be working out the reasons he doesn't want to 'play' with you now & changing them.