i bought an engine 6 cylinder for a 1960 chev bel air the person i bought it from told me it was the same as what i had now i"m trying to change fuel pump and it is not the same mine has long arm in back and the other has short arm is this possible there is 2 type of 6 cylinder and will this hurt the engine if fuel pump is not exactly the same can i install in my car thnks