@Boilermaker1 I'm concerned that even if you find a converter with a narrower form factor, the heat radiating off your heat sink would warp your plastic shell. I would imagine that it HAS to be firmly in contact with the metal chassis.
Most of you have seen my rants about rubber tires in 3-rail O gauge. Ask yourself: What would the peak current draw be if the wheels were allowed to slip, as God and Sir Isaac Newton intended? Perhaps 3A is sufficient?