It just a matter of running a length of masking tape from the tail to the cowl on each side of the fuselage. Pick a spot to start and another one to end...stretch the tape taut and gently place it. That's how they did it at the factory.
Its a simple straight line...just as I did on my P-47 Fire Boss. I use a length of masking tape mirroring the same location on each side of the fuselage. Once masked, gave it a spray with flat black.
