<VV> Steering woes

[James Cuneo]

Hi guys, I have a 65 corsa with quick steering box and Ieco quick steering arms.Other than the effort at low speed, the steering is quick enough.Suspension components ie: ball joints,bushings,pitman etc. have roughly 15k mile on them and are tight.Problem is, steering  feels very numb on center and is slow to react initially. Once in a turn things feel ok. I got under car and observed while wife turned wheel and noticed that the box and frame member where attached move noticeably before any motion is transfered to the linkage.I cannot see any cracks or problems with frame. Is this twisting motion normal? Is there a way to stiffen the frame member?Thanks for any help,Jim Cuneo  Sonoma County CA