Rather than gap massive every 50 hrs, I would recommend replace with Champion fine wire plugs. Massive only last 3-400 hrs before they would fail wear limits and they seem to have about doubled in price in a few years.(more than exchange rate change anyway)
That indicator behind the brass plug is not allowed to be used for timing any more due mandatory bulletin.
Been a few contact points funny wear in recent years on both Bendix and Slick recently, this normally a few hours after 500 hr inspection or O/H.
Cleaning inside where HT lead goes is often missed and can make a big difference in resistance.