Indeed aware of all that you've said, personally I don't like kit bashing as a method because buying brand new models to chop up is expensive and not worth it.
Second hand models are of varying quality and not what I want to offer my customers, and not to mention on a regular basis manufacturers adapt their tooling for a variety of reasons. That means modifying CAD work.
I've opted for a slightly expensive solution and that is having the chassis custom built. It means there's a standard set and something that is fully built to my specs. Something worthy of the dollar bills.
Come this August work will start on my HO scale WDM-2, the WP is high on my list too, so high that I've already done in in T-scale. What I'm looking out for now is suitable wheels and someone good at etching motion gear. See the link to my T-scale WP.
If I fail in sourcing wheels and motion gear I will actually look out for American or European spares, why? Simply because Australian steam locos are almost always limited edition and brass made and hence cost a bomb.
I've also added an image of my HO scale SAN DL700 Industrial shunter used by many Indian industries.