here is a good article with info on steering effort etc.
http://www.carcraft.com/techarticles...ade/index.html
I put an IROC box on mine (same as GTA) and like it, it is a little stiff though. I'm not sure what the NAPA box is, but if it is a direct bolt on it sounds great (all of those listed in the article are direct bolt on to the frame, it is the lines and rag joint you have to worry about). I had to purchase the Lee kit to adapt the IROC box, not a big deal but more money. Rag joint was very expensive but mine was 40 years old and greasy.
My car came with 2.5 turns lock to lock but it was worn out, and was far too easy to turn (very little steering effort). Something to consider is whether the NAPA box is like my old one with little effort, or if the valving is improved for a modern feel?