Nasty, it is possible it was a HYW dept tractor, but in the 50's & 60's it was very common for industrial versions of the tractors to be all yellow so it could have just as easily been in private industry. The older MFs had a 2 tone paint scheme (red over grey) the industrials would have been all yellow. Probably had beefed up hydraulics or multiple pumps, some brands eliminated the 3pt and/or PTO on some versions to accomodate a fork lift of other specialty rear implement/purpose. Often the industrials had beefed up castings in some area as well.