I have seen Airport 25s that were built on both 70 std and 70 industrial chasis.  The serial numbers will tell the difference, but the tags will say Airport 25 on them.  The same is true of the 70 orchard models, as some were built on the standard chasis, and some on the industrial chasis.  The only info I have come across leads to the belief that there were so few of these models built, that when an order came in, they might have pulled the next one off the production line and built on what ever was next available.  I have a 50 that was not built as an industrial, but as a rice field tractor, and uses an agricultural serial number.  I have not had much luck finding out anything on this one either.  Terry.