I read that entire article a few times and applied some of the information to my truck. My 351 has topped out at 18 MPG on the highway. But, that's Canadian gallons so probably closer to 15 or 16 US. That's pretty good considering it was only getting 9.5 when dad gave it to me.
For what it's worth, the article also mentioned that simply replacing the standard air filter with a freer breathing one made a difference on low and midrange power. However, when they put on a K&N high performance kit (similar to a pair of cone filters) that used air from under the hood the huge amount of air available was able to offset the lower density and provide a horsepower boost at higher RPM. It's not stated clearly in the article but it's stated in one of the sidebars. I missed it the first couple of times I read the article.