The PAVN guys look badass. You can also use the Brodie Helmet as a stop-gap Type 58 Chicom Pith Helmet and you can add some tape over it or other material as a helmet cover, since your figs are good from 1965-1970.
Nice collection I was thinking that you could use the fodder Rex body and head and bit one of the helmets on it and make a costom. That could look cool just an idea