Your model looks good so far - keep us updated!
I have one observation regarding the kit you used: Is it just me, or on photos of unpainted model, before the extra armor was attached, it is visible that the middle section of front upper armor plate of the hull (in front of driver's hatch) is noticeably "thicker" than parallel plates on left and right of it - the plate is not flat across the whole width of the tank, but there is noticeable step between middle and side plate sections.
On production Challengers the upper front slope plate of the hull is flat across the whole width of the tank. Only prototypes had the middle section thicker with steps between sections. Tamiya 1/35 Challenger model was based on a prototype and it looks that Revell's 1/72 Challenger is another shrunk copy of Tamiya 1/35 kit
The same is true for their 1/72 M2A2 Bradley kit, which copies all errors of Tamiya 1/35 model.
To be absolutely sure I would have to see the storage box attached to the rear of the turret - it is another part that Tamiya based on prototype and it did not match the shape of the box in production vehicles.
Regards,
Pawel