Barry - there are some key items to note on Tracy's setup of that Subaru as far as I'm concerned, because I've used them myself on my vehicle with similarly remarkable results.
Tracy was able to fine tune his carb (fuel delivery) post-groove. He also made some not insignificant ignition upgrades to burn the groovy air-fuel mix more completely. The friction reduction treatment was also important (Ron's cooking something special up for us that he promises will beat anything commercially available that I'm looking forward to).
That said, if you're like those of us who come here to reduce your fuel usage, once you achieve some gains, it's tough to stop going after more.
Enjoy the ride!