Very nice, glad that you did your research. But I would have to take issue with "The two-wheel trailing truck on this design is arguably not necessary at all... I included it merely to stabilize the “hunting” motion of the rear-facing cylinders, and perhaps to better distribute the engine’s total weight."
I would argue that it is absolutely necessary. Those cylinder castings are heavy, no matter which model loco it is. They would invevitably need support. If the cylinders were much smaller closer to the drivers, ie between the frames and centered above the first axle as in the Southern Q1 0-6-0, then elimination of the support axle would be possible.
As a matter of possibilities, looking at your 4-6-0, I would figure it would be more prudent to give it a deep/wide firebox than retain a narrow pit. It has already been established that about 50% of all heat absorbed by boiler is from the firebox, thus maximization of such surface area would be preferable. We now have a Hudson's trailing truck, so let's use it!
Otherwise, waiting for more!
I believe that your advice regarding the cylinders, although logical-sounding enough, is a bit unwarranted. I do not believe that a large set of cylinders requires a truck of any kind to support it-- for example, refer to the Union Railroad’s large 0-10-2s: hawkinsrails.net/lagniappe/grp… . Other railroads converted locos to do away with their lead trucks, too: www.steamlocomotive.com/santaf… -- and who can forget that the earliest American Mallets were huge 0-6-6-0s: www.calvertcentral.com/RR_OldM… ?
Regarding the 4-6-0: well, of course you are absolutely right that a wide firebox would have been a more efficient choice than a narrow one given the space available. You are talking to the king of firebox aficionados here. XD However, my goal was to portray a design that was likely to have been built around the Turn of the Century, when narrow fireboxes were still largely in vogue-- I wasn't trying to design a thoroughly efficient engine based on modern sensibilities. Remember that the "modern" Superpower firebox, as used above "a Hudson's trailing truck," wasn't developed until 1925. Again, the four-wheel truck on my 4-6-0 is designed as a simple guiding lead truck, not as a firebox-supporting trailing truck (two very different concepts).
Thanks for the great critiques-- I love this kind of thing. ^^ Hopefully you will indeed be seeing more from me soon!