The new Atlas SD45 appears to be a ground up design - it would be nice if the sideframes were interchangeable with the earlier Kato SD45 and Atlas SD35 sideframes (I did this with my Kato SD45s to approximate the "triple' hi mount brake cylinders as found on N&W 1765-1814). Looking forward to seeing one soon - if the swap is simple, I might spring for #1757 as I have ample hi-nose bells in my parts bin.
I might be able to approximate the trucks on 1757 using an exacto knife. 
Looking at the photos on Mark's site (Spookshow), it looks like the truck sideframes are incompatible with the ealier ones:
http://www.spookshow.net/loco/atlassd45.htmlBut, there is a silver lining to being off from work today - I looked at the Atlas (crude) parts diagram for the new SD45 and it looks like the brake cylinders are a separate casting.


This would make modeling the earlier NW SD45s easier - I might just get me a #1757.

I have the bell in my parts bin (but not the whistle!)
Mark