340 4 speed duster throwout bearing arm rod ?

if you get the steel ball from a truck clutch installation
you can replace the flat washer and rubber insulator
they work with the exact same nut
the lumpy locking bit fits into the back of the steel ball which has a cone shaped recess that locks the nut.

you then don't have rubber insulator softening due to header heat

its all spelled out by Mr E.Berg here Mopar Clutch Linkage Solid Steel Swivel A833 340 440 Dart Coronet GTX R/T Cuda | eBay

issue with this is...
1) you must get the push rod on the right way. the D shaped loop is offset
2) the set up is less forgving if your z bar is not quite right i.e the lower fork is twisted
3) it will not work if the Z bar Half moon bush retaining U clamp style clip is broken and the Z bar has slumped in towards the bellhousing

Other than that top upgrade

or use an australian one with the much fatter round rod, 2 lock nuts and unique to Oz washer its a bit more robust. still suffers heat soak in certain circumstances but original rubber doesn't seem to mind .