I don't know if all this is true, but from what I understand Acromegaly is a condition that humans and cats get and it is a benign tumor in the pituitary (in the brain), that causes excessive growth hormone, meaning I think even though he's 11 almost 12 that he may become bigger, and it affects how his natural insulin isn't quite enough and he needs extra insulin and that's why the diabetes.
I have been around a long time, and it used to scare me emensly when I saw a cat getting huge doses because of IAA or Acro. Well, now I got one.
As far as I know, the treatments are brain surgery (through the roof of the mouth? to get to the pituitary by a very specialized vet surgeon) SRT (radiation) which involves anesthia, or a couple of drugs that humans use and can help cats too.
We are wishing The Best for them to help Jackson too.