That's the casting number on the timing cover with the 6059. It has it's own casting number as most engine parts do. Check for the casting number on the side of the block. Also below the
oil filter adapter mounting pad is the date code for the block. Look for a number/letter/number(s) sequence. Also on the heads between the center two spark plugs you will find the head casting number. Above it under the valve cover is the date code with the same sequence as the block #'s. Check to find these if possible. Good chance you will need to measure the bore and stroke as the FE used the same casting numbers on several different blocks but some stand out as paticular applications. Good luck, G.