if it is flying fine with the 50Sx why change it? then you may have to rebalance because of the weight difference. You will also have to get a different fuel tank because of the pressurized system.

Now if you bought a new rocket ship and it needs the 50SX, then you might want to consider the YS63 and the changes to make it work. Although they are a little more money they are great running engines once you dial them in. Plus you may need different fuel for them. I have 4 of them (1.20, 1.40L, 1.10 and the .63) and I am using 20% nitro Magnum fuel. They run like a top.