The Standardised War-Time Jeep, 1941-45 by John Farley.  This is an excellent reference book that tries to show all of the variations of the MB and GPW throughout the war-time period.  Mr. Farley does a pretty good job and the book is well worth owning.  You used to be able to buy the book through  and  it is still listed (through the link provided above).

  • ISBN-10: 0953447030
  • ISBN-13: 978-0953447039

However, the book appears to be out of print as the price is $200 through third party sellers.  Good luck in finding a copy!