Well, I can tell you that coupe doors saves you appx 70lbs right there...

The rigidity is an issue but a nismo powerbrace and some creative welding/bracing will fix alot of it.

If you go coupe doors there is a writeup on the NICO Vert forum on how to reweld S14 seatbelts into the factory location on the chassis. If you have any questions just let me know as I have done all the above things.

Also, Invest early in a new top... I wish I had... it's the one thing that I am embarresed about my car...