Hmm... so apparently 03-05 WRX heads ARE big port heads, 02-05 STi heads are small port. WEIRD! Just did a Google search and all info points to that.

Either way, I don't think you're gonna have too much of an issue with your heads, running decent size cams (272's mate, DO IT).. make sure you port and polish!

Like I said, Sean runs MY98 WRX heads, and Tino runs STi ("small port") heads, albeit modified. They both have big boost and big power, so I don't think you're gonna have a problem with them.