No flack jacket required...I did the same for about 3500 hrs of piston single and twin flying, both normally aspirated and turbocharged, in 'the good old days'...but then we knew no better and all cylinder monitors had yet to be invented.
In PNG we were nearly always above full throttle height...taking off at MTOW with 23-25 inches being all the MP available was something you did 6-10 times a day. Knowing how to lean the mixture in the first seconds of the ground roll was essential to longevity...your's not the engine's
My early instructors treated the mixture control as a normal control to be understood (within the constraints of the technology of the day) and used the way any other control is...not as though red meant 'don't touch'. Any modern day CFIs allowing/encouraging such ignorance, and there clearly are a number judging by this thread, are guilty of negligence bordering on criminal...there is just no excuse when information of the type in Deakin's articles is freely available and has been for over 6 years.
Even if the aircraft you fly does not have the latest injector/engine monitor technology the information is still essential...so you know what
NOT to do....and more importantly why.
EDIT for Sunfish Just click on the link in OZBUSDRIVERS post on page two, save it to favorites and then read every article down the right side of the page that link leads to. Some will take a LOT of thinking about to understand..when you do understand the bulk of what is in those articles you will be a better pilot than now...you will know more than most instructors. From an engine handling point of view you will have every aeroplane you are ever likely to fly covered...he also covers a hell of a lot of basic airmanship stuff. Based on reading Deakin's stuff after meeting him years ago I fitted Millenium cylinders, Gamijectors and and EDM 700 to my IO550 equiped Bonanza when it was having an engine overhaul. I can personally vouch for everything he says....it works, I see it work every time I fly my aeroplane.