Went to dealer to check service engine soon

If the mileage is avtually 140,000, I am assuming 14,000 is a typo, then I would save your money for an engine rebuild which you will need in the near future any way depending on how car was maintained and treated. Not worth spending what is almost half a full engine rebuild on a fix on one head. The price sounds a little high as you should be able to get both heads rebuilt for about that much plus parts.

Mustangs are well built. You have what is called the PI or power improvement engien which there were a lot of them made you can probably get a crate motor from Ford racing for $5000 and remove and replace it yourself with some help from harbour freight tools like and engine crane and engine stand. It is not as ahard as it seems, but litle parts add up quick. But then you will have a car, well maninatianted with a better perform aing engine made by Ford, no one makes them better than a manufacturer, and you can fix all the little things wrong and have done it yourself for under $6500. A lot cheaper than the new stang and I bet you eat em up all day long. Look to summit racing and search anything mustang performance online and you will get some ideas on prices.

No problem. Let me knwo how it goes.