Our CD Lister 8hp started out that way, frozen pump and rack and the injector as an unknow stae. I soaked the pump for some time and found some exploded views of the pump so I could try to put it back together to look the same as the picture. This, for me, (learning about a diesel) took a few attempts but in the end I won and it started pumping againa nd the rack was free and moving. With the injector it too was soaking for some time and all I removed was the nozzle and a little valve of some sort in side and freed it up and put it back together. Luckily for me it worked and now the engine starts and runs.
Hopefully yours will have the same outcome.