I would agree, their rail gun was good enough at a good price for what is mainly a static model. At that price, I can buy two cranes (often needed for a heavy lift).
I do loads of heat shrinking. I always use a mini heat gun. Cheap enough from AliExpress. https://www.aliexpress.com/item/32775611542.html?spm=a2g0o.order_list.0.0.56011802hyUakH
The roof curve starts at the top of the drivers door, the top of the front windows are around 4" below that line, but something is amiss, probably the windows are too low because as been stated the front is too deep.
Don't think I have the instructions any more, but it is not a particularly hard kit to make. Yes the X04 motor does intrude into the cab, but not a lot and can be covered by a back head.
Hornby might just make it work if they used their trick leading pony wheels like the L1. Mine will just about go around 4' curves, it is more the steps that are the problem on mine.
The capacitor as well as stopping interference, also helps stop sparking of the brushes and burning the commutator. The weight just helps the non powered bogie stay on the track.