Edit post description length for external RSS feed display

[imageconstrux]

I know this has been discussed once or twice, but the threads I found didn't seem to have any answers as to how to accomplish this -

I want more of the post content of the RSS feeds pulled to my feed forum to be viewable. Right now it's around 300-400 characters, and I'd like something more around 6-700 characters. I've looked through external.php but don't see a place where I could edit to make that change (however, my php skills are even less than weak).

Has someone done this before? Are there a few logical places I should be looking to make this adjustment?