Now, I'm after a bit of advice. The kit has a semi-circle cover for the brake handle that intrudes quite prominently into the bunker. I've looked at pictures of the bunkers and cannot see any sign of this cover. Admittedly the pictures I've seen are not that clear! Is this definitely correct, or is there another set up?
If you're going to finish the S100 as a pure USATC version prior to sale to the Southern then no, it shouldn't be there.
It is a Southern addition when they fitted standard vacuum brakes prior to entering into service. In most photos it cannot be seen as the SR also added coal rails to increase the bunker capacity. It will be in the first series of modifications viz. vacuum brakes, coal rail, new cab steps, square cabside windows and a SR style throttle/regulator
inter alia.
The modified spectacle plates, resiting of the clack valves from the top of the boiler, Ashford injectors, wooden cab floor, roof ventilator followed in the second round of modifications.
The revised smokebox steps and fall plate were in the third round of modifications.
Quite a complicated history which requires several sources to piece together.