You can try rebuilding the pump but Erps doesn't think that you will have much luck. I hope you do.
You can also look up the Kubota engine block # as in: History of the Universal Motor Company 4
From the link: "The Model M4-30, also called the Atomic Four diesel, a 52 cu in, 25 hp, 4 cylinder, based on the Kubota Y-850 block, was built from 1988 to 1997. Approximately 470 were sold. The Model M4-30 was offered as a diesel replacement for the original Atomic Four gasoline engine. It was similar to its namesake, since it was a 4 cylinder model weighing slightly less (122 kg / 270 lb as opposed to the originalís 150 kg / 330 lb with reduction drive - the M4-30 was only offered with a reduction drive) and generating slightly less power (18.6 kW / 25 hp at 3,600 rpm as opposed to the originalís 22 kW / 30 hp at 3,500 rpm) with a smaller displacement (850 cc / 52 cu in as opposed to the originalís 1,065 cc / 65 cu in)."
The point I am not making is that with the Kubota engine block number AND a tractor model you can find the same pump for a lot less at a Kubota dealer. Maybe not the same exact pump but it will work for a good while.