I had his recipe for gum paste that used egg white powder like 10 years ago and i cannot find it.

 What is the equivalent egg white powder amount to the fresh egg white he uses?

I do not have the original recipe, but here is the rule of the thumb for powdered egg whites: 

Equivalent to 1 egg white =  1 Tbsp dried egg white powder + 3 Tbsp water

Good luck!

When I was teaching, In class I demo'd  making Wilton frosting using meringue powder and being one that I HATE waste I ended up turning it into NL's gum paste.  It worked just fine.   I no longer have the original recipe for either type of icing :(  I'd love to find it,.  Guess I'll try ole reliable Google :)