From what I've been told (I don't know a ton about evo's, mostly know a ton about suby's) that the internals are good to high hp. Might not last for long, but you can do it for a while. Standalone system? Are you talking engine management or what? Cause you can opensource that shit easy as hell now (RomRaider and EcuFlash).
From what I've heard, big turbo, piping, cams. Expensive, sure, hard to do? Not at all. Those things aren't bad compared to an engine rebuild. Could do all that in a weekend pretty easy. If you're rebuilding internals as it is, your chance of throwing a rod deminishes.