Vauxhall Monterey steering box wander

I bought this Monterey as a cat C accident damage needing front end repair. After stripping off the damaged parts I found that the steering box had took a hit and twisted the splines so I changed it only to find this one wanders all over like driving a boat. I adjusted the nut and screw at the top which did improve it but now it will not adjust any further due to the screw being siezed. What I wanted to know is if I can take out the screw and nut in one piece so I can free it on the bench to save taking the box out. Is it spring loaded ?, will it go back in easily ?.
By the way I have arms like Popeye and fingers like pigs t@ts so neither way is easy but removing screw is easiest option.