Y'all have me thinking (for a change). I haven't touched the numbers, I'll
admit. I erased the original message but could have sworn that it mentioned
bubble tail lights. My 56 has these and, correct me if I'm wrong, they were
changed to flat in 58. I would assume that the 57's had the bubble type.
Would that make the bus a pre-58?

 Raul
 Wilma  (1982 Westfalia)
 Larsen (1956 Microbus)