1988 over heated and now knocking
 

I let my girlfriend drive my 88 f-150 w/302 and she had it in low1 drive and it over heated. When I came to my trucks rescue it now knocks. I've been told that the lifters maybe stuck so I've put Lucas oil and put SeaFoam in the oil. The oil gage is still jumping back and forth and it has a slight knock to it still please help me! I've been told that it's not loud enough for the bearings to be bad and that it might be the oil pump is going or gone bad. I need some Good ole honest help with resolving this!!