1 - The odometer in those cars only records to 99,999 miles, so it rolls over to 0 again every 100,000 miles. It's highly unlikely that a rusty '77 car sitting in someone's yard only has 87k original miles on it. More likely the odometer rolled over and it has 187,000 miles... or maybe even 287,000 miles if it rolled over twice. Since there's no requirement in Minnesota to even list or verify an odometer reading upon sale of a car anywhere near that old, don't pay any sort of a premium for it being a "low mile" car because there's absolutely no way to verify the odometer reading.
2 - That car will get bad gas mileage. Like, really bad gas mileage. I'd expect it to get somewhere in the neighborhood of 10-12mpg if it's running at all right, and possibly half that mileage if it's not running right. Fueling that car is going to hurt even if the sale price doesn't.
3 - It'll almost certainly never be worth more than the $2700 the seller is asking for it right now. Just because it's old doesn't make it a classic. And if you've got any aspirations to "fix it up", I'd forget about that unless you're okay with spending a bunch of money you'll never get back later.
I'm not saying absolutely "don't buy it". If you really want it and are okay with that price (or can talk him down some, ideally), it's your money do what you want. Just know what you're getting into before you buy it, that's all. Good luck.