What to do with a dog aggressive senior?

So I rescued an 8 year old cattle dog/pitbull mix not too long ago. He’s an absolute sweetheart, until there’s another dog around. I was misled by the rescue agency about how badly he reacts to other dogs and how unsocialized he is.
Whenever he’s able to see another dog he loses his mind; if it’s through a window or from the car he barks and growls excessively, if it’s up close he snarls, barks, growls, and chokes himself out on the leash trying to get to the other dog.
He grew up on a 60 acre ranch able to do as he pleased day and night, spoiled as a dog could be but he was only ever around his sister so he’s completely unsocialized as far as other dogs are concerned. I was told he was attacked by a pack of dogs at 2 years old as well.
I’m really desperate here, I know he’s a good dog and would really benefit from less anxiety and aggression but I don’t know how to go about helping him. He’s never bitten anyone or any other dog, but I’m scared there might come an unavoidable situation that causes it to escalate. Does anyone have similar experience/any advice for helping to correct this?