Hi Jon,
Yes the Mk 1 eyeball is remarkably accurate but you must check and double check. Do one side first and that will be easy, the secon side is the one that takes the effort as you have to match up the two sides. Look along the model, nose to tail and visa versa until you are sure everything lines up. Like I said the first piece of masking is a doddle, so you should just be repositioning the second piece.
To make life as easy as possible cut the tape into thin strips, as it will conform to the shape better. Tamiya tape is a bout the best you can get but, unless you have it in a dispenser I recommend cutting a straight edge to it ( I have mine in a dispencer and still cut the edge). This is not to say that it usn't straight but the roll will pick up fluff and dust. I pull a length off the real and stick it to a piece of glass, then cut with a steel ruler and a scalpel. When these thin pieces are on burnish the edges down, a thumb nail works well, then, using cheaper tape, mask over the tamiya tape to protect the rest of the model from over spray. The Tamiya tape is used to give the best clean edge possible.