I've upgraded my NT-16 with the 18 size piston, sleeve, and connecting rod. (CEN Piston and Cylinder - G70344-08, CEN Connecting Rod - G70344-07) I just wanted to make this post because I've had excellent results with the modification.
From what I read before I did the modification, I was under the impression that I wouldn't really see to great of results. My particular results have been great. My truck is performing simply awesome. I'm running temps of 220 to 240 doing full speed runs, running in the grass, and just plain running it hard. I've noticed a change in power in my low, mid, and high range. I'm hitting second gear at just above half throttle! Before the mod I was running full throttle for a few seconds before second gear was kicking in. The second gear hasn't been tuned since I've upgraded my engine. Before the mod, I was really pushing my temps to try and achieve the performance I was looking for.
What i'm getting at is... TRY this upgrade! For $35.00 I'm more than happy. Now I must go play some more!!!