Chris, thanks for the information.  There is no suffix &quot;C&quot; number, as a special gearing option, but there are a couple of numbers in front of the serial number, which are very faint, and look like they must have been stamped later.  Looks like either 35 or 3C, not very clear and can't make out the second number for sure.  After scratching around on the frame, there does appear to be green paint under the industrial yellow, which show up best where the mounting pads were welded onto the frame.  Your thoughts about the different gearing on a standard make sense.  I have not seen a heater mounted under the dash before, has anyone else come across one of these?  Is it either a factory option, or a Lull item?  Thanks for all of the help.