sodium valve stems, where i ran into them was hyster lumber carryers,and scajet log loaders,.292 in career and302 ind (lincon)style y in upper. that was used for yarding logs.the lumber carures where on propane. what we wher told that if stems wher broken could explode(wher making a punch from a old thick stem ex,think that was a storey to scare us.scajet was a logging equ. manufacture co in cdrawiley wa. i would hesitate to use them in a car.  if any 1 needs a 292 i have a 1957 block and crank and rods,std bore and crank.300us but in bc near the border.

Years and years ago when my dad worked on old war birds he talked about exhaust valves filled with sodium and how they would dispose of them at sea. The sodium was to keep them cool .