It's Subaru! There was a Leone on TradeMe (NZ's version of Ebay) that had done 494,000km on one engine! And there are many and sundry original Legacy turbos with 200,000km that are still fine. To be on the safe side, I'd probably replace it at 100k miles. Although worst case scenario, you have to rebuild the engine, which frankly isn't that bad... Yes, mods like the ECU are best done professionally, as is porting and polishing, but it's really easy to fit turbos, exhaust, intercooler, etc. You might want to do a bit of research on your block.