Great work on an interesting project. The NYC suburban service loco is a late built Forney type, perhaps out-shopped in the early 1910's and perhaps modernized somewhat by the 1920's.
The engineer's side would also have air reservoir, perhaps a bit shorter than the one on the left, or fireman's side. There would be a reverser rod, leading from the cab to the valve gear from under the cab floor. Or, perhaps even a power reverse unit.
That type loco needs a rather large radius curve for good operation, because of the extended rear overhang, as you noted. While a small loco, it's wheelbase rivals that of a 4-8-4! Your ideaof removing the flanges of the rear drivers and making a kingpin pivot for the rear truck will enable a tighter curve to be run.
However, may I recommend it may be best to remove the rear driver's flanged tires and install new blank face tires that are a wide as possible to fit witout touching the frame. That would help the rear drivers stay on the railhead, and not slip off to the side on a curve.
If they do that, even with the rear truck supporting the loco, there could be a derailment if the rear driver tires cannot climb back onto the rail head.
I'm also working on a Foreny type loco, in my blog "Making this from That." My model is set to run on a 62" (5') minimum radius hauling as well as backing at least two 60' (15") passenger cars from the front as well as back end. The rear truck on originally slid back and forth sideways. That model was oriinally built by Gem of Japan in 1972.
I had problems in backing a train with that sliding rear truck, so I changed it mounting to a trailing, pivoted tongue, like the front pilot wheels have.
My model, which has taken a few months to work over, is almost ready for paint, striping and lettering, which will be done in the prototype's 1890's fashion.