If we are designing a single seat twin engine fighter from scratch either with the V-1710 or R-2800 engines, we would probably lay out the internals quite differently than we would with the idea that we are trying to keep the appearance looking somewhat like a P-40 or P-47. The question is really how much of a change in appearance are we willing to accept and still call the result a "Twin P-40" or "Twin P-47". Just tacking on an extra engine to an existing airframe doesn't work because adding a couple tons of extra weight in the nose of an already "balanced" aeroplane generally doesn't do good things.
The actual mock-up for the Twin P-40 had lots of problems from a practical standpoint. There was no room for extra fuel in any reasonable location. The wing area did not grow for an aircraft likely to weigh about a ton and a half more than a standard P-40. The horizontal and vertical stabilizers did not grow which would be interesting for stability considering how much more airframe was now ahead of the wing. P-40s were already having directional control problems with the higher powered engines to the point that extensions were added to the fin in some models.
With a twin setup, getting both propellers to rotate outboard would help as long as you didn't lose an engine at low speed.
Another issue from an appearance versus practical standpoint is the location of the engines. It is a given that the view from above will not resemble the original nor will the view from the nose. If done properly, the view from the side CAN look like the original P-40, but causes some problems. A high cowl line is needed for appearance but is lousy for visibility to the sides.
With the Twin P-47, as we already agreed, without an engine and ducting in the fuselage, fuel doesn't need a fat fuselage. Guns and ammunition are heavy, but don't tend to take up a lot of volume either. Now a piece of equipment that might be an excuse for a bigger fuselage is a radar installation in the nose with a nice battery of guns in the belly.
