According to the Service Bulletins, K-F engines (including the 226 with dual manifold and the supercharger) would run ok on regular gas, if timing and other things were set up correctly. The 79 Octane rating in the bulletins was caculated by a different means than as shown at pumps these days; using the current formula, the octane need is in fact 87. Further, if you check gasoline (different brands) at random, you will find that some different brands are identicical in some states as laws (such as in Wisconsin) allow owners of gas stations (independent ownership not owned by an oil company) to buy gas anywhere they wish and sell it as the branded product. As a result, you can find "pinging" in various brands of gas. We used Amoco/BP and did not have any more pinging problem than we had with the FF engine in the truck (that can run E85) or the Lumina (3.1L V-6).
Almost all gasolines these days use 8-12% alcohol of various types as an additive.
To be on the safe side, when rebuilding an engine (not just K-F motors), install hardned valves and hardened valve seats. The exception on the seats are Ford Motor Company vehicles built starting with the Model A Ford motor; Henry Ford had the company induction harden the blocks as part of the regular production process.