1961 170 Slant Six

Ok here we go. I have a 1961 170 slant six from a Dodge Lancer. My daughter and I rebuilt the motor, 904 tranny and are trying to squeeze it into a 1966 Plymouth Valiant that had a 170 from the factory that was long gone when we got it. My question is the 1961 170 was missing the original oil pan, but the dude had one laying around his shop, that he included. This oil pan has the number 987 stamped from the inside out on it. This motor won't clear the frame or the motor mounts won't line up. Is this the correct oil pan or do I need another as I have heard. Help me out guys, my daughter is driving me crazy. Thanks in advance.