Peter's advice is good. In my experience way back when, when I got my first Athearn Big Boys, I wanted to shorten the drawbars for a prototypical distance between the cab and tender. Since my minimum layout mainline radius is 24" this wouldn't be a problem. In the process, I broke a drawbar, called Athearn and they sent me several replacement drawbars very promptly along with several other parts that I wanted to update my models to the way Big Boys appeared after 1947. Additionally, they didn't charge me for the parts! However, their parts department management has changed since those early days, so your experience may not be as pleasant as mine was...
Cheerio!
Bob Gilmore