The new body looks great. Looking forward to seeing the chassis.
The body dimensions have nothing to do with how the wheels sit in the rear guards. I bet my CR rear guards are dimensionally about the same as CSX3034 as it's mould also originated at some pont from an original shell. The CR also has the wheel arch lip which I believe is something the Comp cars got along with a larger front flare.
What makes the wheels sit right in the wheel arches with the right dish is the rear suspension design. As most cars use donor components they are often limited to some of the donors dimensions ie the rear track . Many shorten their rear ends which is easy enough if you have a live axle rear or a Jag rear. Some of the more modern double wishbone rear ends are more difficult to narrow to more original dimensions.
With a fair bit of work I managed to pull 4" out of the rear end width on my CR. I like the wheels tucked in under the guards but to do this they need offsets that don't have a lot of wheel dish.
Before:
After:
