You DO need the pump. At 280 feet, get some quotes to pull all the old stuff and replace it with a one pipe submersible pump. Your system is an antique and not reliable or desirable. A 1/2 hp submersible will out perform a 1 hp deep jet pump. By the time you diagnose it, your new pump will be installed.
But if you are a mechanical engineer,you do not need any contractor to do this. Read a few pages on sumersible pump installs and just DO IT.