I have a rather heavy 16' that originally had a YJ. Not very impressive in any respect, but once the shaft started to go the choice was premade. I used one of HiTech's energizers in kit form. Completely satisfied with it in every way. The conversion is simple for anyone with even borderline mechanical skills. With a moderately modified & fresh 455 and AA impeller I am seeing 4650-4700 WOT.
Looking back the YJ would run up into the 5K range, not good with that olds motor, at least in my opinion (which is worth exactly what you are paying for it.) The energizer does seem to be a bit more of a fuel eater, but there is no doubt the holeshot, and top speed have increased significantly.
If you are regularly operating in weeds/rocks/shallows the jacuzzi is allot harder to screw up. My shoreline is full of milfoil out for 300 yds or so. (and the DNR won't let me remove more than a 6' wide path.) the energizer likes to get a big mouth full of salad every now and then, a whole load of fun to pull off the shaft/impeller/loader.
Even rounding up allot of used components is going to rival the energizer's cost. The only concern I would have is the weight of that size hull. One hates to go backward in performance.
All in all, I am glad I made the change.