Engine and trans are basically fine but the Chrysler "Lean Burn" system can be problematical.

A family friend of my father's had that car with the 360. It wasn't terrible for him. He got some use out of it. The 318 is alright.

I haven't seen one of these old Miradas in person before, the closest thing I've ever seen to that car is a 1981 2-door Chrysler Imperial. So it's pretty rare and unique, but unfortunately that doesn't mean it's very collectable. But that also doesn't mean you still can't enjoy it, The 318 V8 while a decent (and underpowered at the time) motor is fitted with the "Lean Burn" system that Chrysler had installed in all their cars at the time, so keep an eye on that since it will probably develop problems in the future. But the Torqueflight transmission is pretty solid.

Though keep in mind the American auto makers weren't making the best cars due to the many things that were happening at the time, so watch out for rust.