I have a 1985 240 DL sedan, and it runs fine, but the body is in horrible condition. The window regulator is all ****ed up no matter what I try to do with it, the headlight assembly needs a lot of work, the spedometer cable is broken, and the body has rust and a big dent.

My friend has a 1987 240 DL sedan that he wants to sell to me that's in much better condition, except for the driver's seat. But I'll just switch my Volvo's seat with that, because my interior is still pretty good. He says that he's put about $1500 worth of parts into it, and after taking it to a foreign car repair place, it ran for a short while. And then it stopped working again. He says that one of the last things he hasn't switched is the brainbox, but I guess he's too frustrated and broke to want to try to fix it some more.

He said that he'll sell it to me for a couple hundred, so I'm going to offer him $350-$500. From what I've seen, everything's in excellent condition. Since my car runs fine, the brainbox should be in good condition, so I wouldn't have to spend any extra money. And even it if isn't the brainbox, I could just switch out the entire engine from my car into his after I buy it.

So here's my questions:
Would it be worth it to buy it, even if there's a chance it might now work?
Does it sound like the brainbox could be what's causing problems?
Will the 1985 240 DL brainbox work with the 87 model?
How hard is it to completely replace an engine in the 240 DLs?

I'm graduating from high school on Wednesday, and I really need to get a working car. Please reply with any valuable information as soon as possible.