Should I trust the sodium filled valves for my SOHC?!

I have an all original Holman-Moody prepared 427 sohc motor. The fella I bought it from had it all checked out before he sold it to me. It was in a Cobra kit that he had purchased. Holman & Moody received it as complete motor #QEC-7-324, did their liitle voodoo to it and it was put in the car. It has 914 original miles on it from brand new and it ran GREAT when removed a year and a half ago. Before I put it into my 67' Mustang fastback should I swap the sodium filled exhaust valves for stainless? Recently a friend of mine started up a 427 sideoiler that had sat for many years and the sodium valve broke immediately, detroying the chamber and cylinder. I've been told not to worry by some and DANGER by others. Anybody have experience with this situation that could give me some reassurance? Thanks.