WWII liason aircraft guru Ken Wakefield also wrote Lightplanes at War,
published by Tempus in 1999 (ISBN 0 7524 1727 4): a better read than The Fighting Grasshoppers (and less redolent of a minor insect battle), abeit one with indifferent photo reproduction (with the exception of Chris Whiteman's splendid cover air-to-air of my L-4!)
As to swapped fuselages - hmm. At the risk of opening a can of worms, I would say the aeroplane's identity stays with the main fuselage frame, which is the biggest single structural item, and carries the serial number. The French were not so diligent in keeping the correct logbooks with the right machines, so mix-ups are common. They may well have made up bitsas through rebuilding two or more L- Cubs together, and using whichever bits came to hand first in completing the final product. Piper's mass production methods should have ensured good parts interchangability.
As I am not sure it would be right to post his address without checking with him first, If you would like to send a private message to me, I will forward it to Ken Wakefield.
P.S. Maurice Brett's old Aeromodeller scale drawing is a first-rate guide to markings, for those wishing to paint up their L-4s authentically.