I really like this project, and love seeing how it comes together, but personally I would not have gone through with it. From experience, I can say that if you have patience and look hard enough, you can even get 12v trains in pristine condition, for cheap. When I bought 7740, it was dusted down and looked very dirty. But after wasching all of the bricks, it came out just like new. Comparing the bricks to new bricks, there is no difference. At all. And I've come across finds like these before, like my 7727. The thing about trains is that they're often only built once, and never taken apart.
But if you want the feeling of truly new bricks, I guess this is the way to do it. Can't wait to see this finished :)
I'd also like to add something concerning the texture of the roof slopes. It's the same case with many of my old trains, even though none of the parts have been replaced. Also with other slopes like 2x4 and 2x3. So I guess there's no way to avoid it.