Don't think FDR's pvt car would traverse yard trackage due to the car's weight(Armor plating)
The weight was immaterial. The New Haven kept a 230-ton steam-powered wrecking crane stationed at Oak Point Yard, and it occasionally entered and departed the yard through the east end, which meant running the whole length of the yard.
Also way too many sharp crossovers from the Port Morris branch to crawl thru with 6 wheel passenger trucks.
Again, a non-issue. The Port Morris Branch was listed as an Emergency Detour Route for New Haven traffic into and out of Grand Central Terminal.
The only restriction (and the New Haven carried plenty of six-wheel Pullmans and dining cars) was that on certain curves two trains could not pass one another at the same time due to overhang.
I've yet to see a track chart for the Port Morris Branch showing the degrees of curvature for its assorted curves, but they certainly weren't that sharp, maybe 14-degrees at the most. In contrast, the curve at Danbury Union Station was a 17-degree curve, and that saw its fair share of six-wheel-trucked cars over the years.