I think you're making it sound like it's way more difficult than it actually is. The post content is wrapped in the CSS class post, which holds the font information. Here's the CSS file that defines the style of this very page. We find .post:
.post
{
font-family:Georgia,"Times New Roman",Times,serif;
font-size:13px;
line-height:1.6
} All it takes is to change the Georgia part to some other font name.