Reynald's number
Bill,
There are many reynolds numbers associated with your B25. At a particular air speed the tip of the wing has a different reynolds number than the root of the wing. The engine nacelles have have a different reynolds number than the fuselage and the tail. As the air speed changes so do all those reynolds numbers. In a standard atmosphere reynolds number is equal to 68459 times the length in meters (of the flow over the surface), times the airspeed in meters per second.
In english units, reynolds number is 780 times the length in inches (of the flow over the surface), times the airspeed in miles per hour (at sea level). At 5,000 feet of altitude the constant is only 690 because of the less dense atmosphere.
The boundary layer thickness increase slowly with reynolds number decrease.
Therefore, your B25 fuselage will have a somewhat thinner boundary layer than your B25's wing tip at the same airspeed. Your B25's collection of boundary layers will be much thicker than a full scale B25 because of differences in both size and speed.