1978 D100 diesel help!!!
 

I just bought a 1978 D100 with the Mitsubishi 6dr5 diesel. I think it has a stuck rack in the injection pump. I think I can fix that if I can get the pump off. Problem is that I can’t get the pump to move. It slides back maybe 1/8” and then bonds up. Can anybody help me? Is there a trick to getting these off?!