If you looked on the parts store for a discontinued locomotive, say the EM-1, and bought all the parts and put them together, would you have a working locomotive? If so, would it work WELL?
That depends on how thorough and refined your craftsmanship is.😂😂
But this kind of thing is doable?
Also, Mr. Bach man, the picture for the Acela loco shell #2018 is a picture of #2017 just so you know
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=68_88&products_id=10544&zenid=3ald5q68921j1aaa956s873qa3
If ALL of the necessary parts were available, and you knew exactly how to wire it, then yes, it's doable. Like Trainman203 said, how well it would run depends on your skill level and craftsmanship in assembling it.
You're probably better off looking for whatever it is you're interested in on one of the auction sites. Then doing any repairs needed, if any, rather than trying a build from scratch.
Len