Regarding the 59 that has the mechanic claiming a " weak valve", I would hope that the mechanic in question would have the sense and equipment to take the few moments required and take both a dry and then a wet compression test of the cylinder in question before making that diagnosis. As far as the metering rods are concerned, the FSM of that year car should list the size of rod used, and if newer ones of the same size are not available, then some used ones would hopefully be found. Good luck! Mikey 62 Crown Coupe