***Can I successfully run lean of peak in my bog standard O320 or IO360 etc with just a single point EGT or even no EGT?***
Yes. If one leans from Best Power until there has been a 3-5 knot loss of airspeed the engine will be comfortably LOP. If the engine is smooth at that point, it assures you that:
1) The F:A ratios are balanced.
2) The ignition system is healthy.
3) There are no induction leaks.
If it is not running smoothly at that point then one or more of the above is begging to be addressed.
***Is this done solely by leaning till the engine runs rough then enriching till the engine runs smoothly just as I was taught many years ago?***
No. Unless you know what the F:A ratio spread is you have no way of knowing when the roughness is setting in. In a very well balanced engine it will never get rough--it will just get to idle cutoff and die. In a poorly balanced F:A ratio condition, it may get rough before it ever gets to peak EGT. Lean to roughness wasn't about engine management, it was about "cabin comfort."
