Regardless of the technology, NGE was not just another giant mecha
series.  What about the Angels, the HCP, SEELE, and all the mysticism and
conspiracies?  So far, your idea sounds more like a mecha series such as
Kishin Corps.

Mmm...  Ever watch any Indiana Jones?  He could try something along
that style.  There is much room for invention, since the Nazi's looted
most of Europe.  Heck, north Africa is a great place to dig up mystic
mumbo jumbo, if you really need to.

In fact, it is quite necessary to do this.  These huge monstorities, no
matter how much armor, could be brought down with conventional weapons,
unless the author totally bends the laws of physics, or goes the Marvel
route (Cpt. America's shield, Wolverine's - now former - metal bone 
sheates) - which is no fun at all...