1985 300SD Motor shot?

[anolley]

As you can tell by post count and member date, I am a newbie. I just bought an 85 300SD last week and have a question or two.

The car will start, but there is a nice banging noise (sounds like someone hammering under the hood) and it will die shortly after unless the gas pedal is constantly pressed.

I also need to know if anyone in the Arlington Tx area knows where to get a good (preferably cheap) replacement engine if this is worst case scenario.