Some 450s used small round injection pumps that have no pellathane ring inside to fail. Parts for those pumps became unavailable in the
eary 80s and Deere sold kits to convert them with later style pumps. So, I have no idea what you have. Here is a photo from another poster
here with a conversion pump on his Deere crawler. If you pump looks like the one in this photo, then you DO have the plastic/pellathane
ring that often fails. To replace it? With the pump off on the bench (or tailgate of your truck), it takes about an hour to replace the
ring and install all new seals in the pump. $25 in parts. Requires one special tool that costs around $10 if you can find one anymore.
Note - that is one hour IF you have experience. If not and you are using the repair manual - it might take you half a day. No big mystery
inside. It is just two hydraulic pumps coupled together with a flyweight governor inside. There is one bolt that has to be removed that
uses a 6 tooth male Bristol wrench. Just about every Deere of that vintage I ever worked on has that 6 tooth bolt head. Other makes of
tractors sometimes had a more common Allen head instead.
Note that IF that ring inside the pump failed (assuming you have a JDB or DB pump) . . the inside of the injection pump reaches too high a
pressure because return fuel cannot get out fast enough. When that inside pressure exceeds charge pressure - it acts like it had run out
of fuel. This happens because little pieces of that plastic ring get stuck in the return fuel circuit and stop fuel from exiting the pump.
Look at this other poster's photo. Is this what you have?