My methods and techniques have been reliable over six decades being a gear-head. Have followed Motor Manuals suggestion of selecting suitable tool. Often, that straight edge proves positive. The trio intake ports may not be absolute. The detent grove in the head / intake port for the ring does come into play when torqued to specs. A milled surface may create problems. Any leak at the intake ports will change the air/fuel ratio to lean and the desired idle will suffer. I like your " satisfactory long-term solution". Leaks suck !
