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