Can somebody give me some info on this steering boxes. Are they compatible? Thanks!

 

If they are both from first gen RX7 yes they are compatible .The one in car is series 3 and one out of car looks like a series 1 or 2

 

With the "new" box on the bench, you have the excellent opportunity to go through it and adjust it. With that box you only have 2 adjustments:

1. The bearing preload on the steering shaft
2. The gear lash between the recirculating ball nut and the sector shaft

You want both of those to be tight but not too tight. If too tight, it feels "great" for awhile but just wears down the surfaces of the teeth and gets too loose to ever adjust correctly. I wrote a very quick take on what I did with my later box (like the one in your car now) which has 3 adjustments. The additional being sector shaft bearing preload. You might just want to try adjusting your current box.
https://www.rx7club.com/1st-generati.../#post12486422

And here are excellent threads I found here, which I based my work on.
https://www.rx7club.com/1st-generati...7-gsl-1114116/
https://www.jimrothe.com/mazda/steering.html
https://www.rx7club.com/1st-generati...again-1153901/

 

Thanks for the info👍👍