Water pump help

I am a little confused on the above. I am putting a 360 in a 67 Barracuda. I am looking to put a thick core and electric fans which I understand come out at about 6 inches thick. With the aluminum water pump I am right at 6 inches so no room for the motor to move around. I understand the early cast iron pump is shorter. Does anyone know how much shorter? Is it worth while? Will it bolt to the 360 timing cover directly? will I still be able to see the timing marks?