[olddog]

I read that Ford did use sodium filled valves on the 427 back in the day (think only on the exhaust). They reportedly did it to be able to run higher RPM via the lighter valves (other benifits may apply). Heads breaking off of these valves were very common. Drag racers of the day had different opinions. Some quit using them others replaced then after a few runs.

Better material and manufacturing practises may exist today. Maybe the old problems have been solved. However these are relatively large diameter valves, mind you. Just because a Porsche can run them without issues, does not necessarily mean they will work on a relatively monster sized valve in a big block.

Unless you are building a high rpm FE, they likely are not needed. Sounds like a risky path to me.