One option is to hop on Amazon and do a search for Spitfire books. There is a pretty huge selection. Most helpful may be books on the restoration of a specific plane. The Spitfire is a popular and therefore well documented plane. "coffee table" books are usually only good for large format photos of currently existing aircraft but a lot of the more detailed specialty books will have nice three view drawings. It is also possible to buy Photo Paks and walk-arounds that provide a comprehensive set of photos for a particular aircraft. If you haven't already, you may want to look in the warbirds thread on this site. The red circles, by the way, are probably the taped over gun port on the wings leading edge. The number of circles will vary with the mark but a Mark I should have four on each wing, one for each of the Browning .303 machine guns.