Deniz, Hi and will be great to see a few more Cr1 builds ! great tank, very underrated.
There are really 3 main issues with doing the desert version with The Tam kit (apart from some soft detailing in a few areas … rear turret bin as mentioned, and the front slope on the glacis plate in front the drivers cab and the 2 cut outs left & right to the rear of the drivers cab (simply fill these areas and re-add the weld lines.
The front slope should really be flat all the way across and not have the initial added armour cheeks - both Russ @rfbaer have corrected this and its really straightforward to do, just requires care and a careful hand.
This is how I did it in my Cr1 CTT build.
Challenger 1 CTT
Its from about post 26/27. If you want it correct, you should not just add or make inserts to raise up the level on the L & RH outer sides, this is incorrect and will give the slope a false height ( although it is hard to see unless you know about it).
Also, make sure you use the later exhausts as well (which need a bit of work to open them up).
Everything else you need is in the kit. The additional turret left hand side bins varied a lot from custom made baskets to Chieftain long bins (full or cut in half) or none at all. I would pick a wagon from an image and do it that way.