Christo, i will help with some answers:
- The extension to the sideframes are only correct on the inner side of each bogie.
Yes, this is correct. I have removed it on the outside. That is the current state (3D-Rendering, part of the first lot):
The shape of this extension seems me approximately correct, exept the openings. There are no openings to get the stability of this exposed part. Further, this is on the "dark side of the locomotive".
The mounting-stubs have not the same stability like the Bowser-originals. Is its better to remove the gear-coverage completely bevore mounting the bogie-sides. Then, once the sides are on its place, you can remounting the coverage without risk to broke something. Same the brake bar has a lot of fragility. Some caution by mounting the sides is needed.