mpg on 1984 chevy truck.

I know it's not a mopar or a a body but this is the only forum I use for cars and I'd really like you guys opinion. I'm looking at this 1984 chevy truck and I'm a little worried about mpg. I know without knowing more about the truck it would be hard to say but I know it's a 350 with a 600 cfm carb. Here's a link for the truck. http://dallas.craigslist.org/dal/cto/4346699613.html
Any opinions would be appreciated. Sry for placement of post. Thanks