They covered their arses to a certain extent by suggesting that if you ran LOP above 75% for extended periods, you might damage the engine.
The caution applies to all leaning, ROP or LOP above 75% power including the quote "if unsure use full rich mixture". There is a statement also in the Warrior manual that states no more than 15 seconds above 75% with the mixture leaned, this is in regard to should the engine power exceed 75% power during the leaning process.
Of course had they operated these engines at 32-34" /2300 and 80dF LOP they would never have had any detonation to damage the plug ceramics. Had they run full rich in the climb instead of skimping (not rich enough) the same would apply.
That's about 80% power at cruise altitude, not sure I would use that higher power setting at 2300 RPM on a J2BD. A 65% power setting would be around 30"/2300 at normal cruise altitudes, 33"/2400 for 75%.
Piper also advocated a leaned climb at 85% power, but it was in accordance with the chart above 75% and basically was min 27 GPH (hard fuel flow limit to 18000') max 1500 EGT and max 475 CHT.
I used to fly these things by the book and they seemed happy, including the min EGT leaning for decent rather than the 2" per minute etc... It would be good to see some monitored data on these things to see how efficiently you can fly them though.