Add coolant overflow to 225?

The type of radiator you have dictates whether or not an overflow bottle is necessary.
Earlier rads used a very large upper tank. These are only supposed to be filled to the top of the tubes, and the extra space is for expansion. You wouldn't use an overflow on one of these unless running it at the track or other situation that called for a catch can.
Later rads, 73 up used a smaller tank that is supposed to be filled all the way, and these use a recovery bottle.
That bottle is actually an active part of the cooling system that transfers water back and forth as the engine runs through heating and cooling cycles.
On a 73-up A Body, it mounts on the passenger side if the core support.