[Farmall] U-1 Cub Power Unit Serial Number

[Al Jones]

All,

I have a U-1 power unit, same engine as a Cub Farmall, on a 52R combine.
The power unit serial number is 580.  (I didn't write down the engine
serial number but it's a '49 by casting codes.)  Did IH begin numbering
their power unit models at 501, like they did most of their tractors?

thanks,
Al