This mini Jesus pendant should fit a 4mm Miami Cuban link chain with a box lock unless chain has unusually thick lock (they come in a bit different sizes), if you are purchasing both pendant and chain from us though we will adjust the bail (if needed) to fit the chain. The 2.5mm chain will definitely fit the pendant without a problem but you are pretty big guy at 6'3 so we would recommend a 3mm-4mm chain for you. Yes, 24 inch is a good length for your height and this size pendant.