I went as far as getting a test print. Here's what I learned
1. Even though the driver size, spacing and wheel base of the spectrum 2-8-0 are very close (cylinders too!) the boiler and cab are way too small to mount on this mechanism. The motor hang out of the back of the cab by several scale feet - I have a pic somewhere

2. I'm not sure that I'm the guy to tackle the belpare firebox. It was close enough for me (a WM guy) but I'm not sure that the Pennsy fans would ever be satisfied

3. I would be all for doing boilers without details, in fact I'm considering this for my next WM 2-8-0. Since FUD is a porous material I don't think that it would be possible to make an adequate casting from a 3D printed object
4. With a little care, and some very fine sandpaper, the stepping and textured surfaces an be taken care of. That coupled with brass and etched details can make for a very stunning model. I have done this treatment on my diesel conversions and am very happy with the results
5. I wanted to try the M1, I really did, but see lesson #2. I have a few more projects I want to do, maybe if my skills improve I'll look back into the Pennsy projects
The N6b will be available shortly, I'm waiting on test prints so that I can fine tune the coupler height.