I really like the look of that!
What did you use to glue the extra section on to each truck (to get 4 wheelsets per truck)? Kato frames are probably Delrin and I don't know what you had the Shapeways parts made out of, but I would think it would be hard to get any glue to hold those together.
On all driver and end truck sides I use a large auto file to completely remove all detail for a smooth finish. On the Shapeways side covers I hold them flat on a section of 320 sand paper and sand them thinner as well as smooth.
Like most all Shapeways engine shells, they also come with the side covers for driver sets as well as end wheel sets.
The Shapeways side covers I glued first to the GG-1 sides first starting at the rear sections., then aligned and glued the 4th driver set as a free roller.
When I built the Great Northern W-1, I was testing different types of glues.
I found by using Testors model cement to hold the pieces together untill dry, followed by Krazy Glue using the tip of a small wire and applying all around it held like concrete.
One of the Shapeways W-1 side driver covers was a bit crooked so I had to remove it to align. found out it took quite a bit of careful use of an Exacto knife and some time to separate the parts.
Another glue I use at work is J.B. Quick 2-part plastic epoxy glue. With this glue, best make sure everything's is correct as theirs no removing.
This was the last glue I used applying the same way as Krazy Glue, now their all permanent.