Flew my Aerostar without engine monitor and LOP for over 2 years. No problem. I practice the "big pull", to get over the Peak quickly. I always cruise at power settings below 70% even though it's turbo'd. Pull until it slows down about 10kts, but before roughness.
In fact, the old-timers flew the radial old piston airliners like the DC-7 and the Connies just like this, by leaning by feel and exhaust gas color.