I have a warner box in the bench vise ready for a rebuild. I have rebuilt 3 servo boxes. Other than the brass synchros and some extra cer-clips on the fork rods, I cant tell them apart. As for performance, I was driving the warner box in a 70 SRL until it would not shift into 5th gear. (Caused by Loose locking nut). I put a rebuilt servo box in that car. I cant tell the difference between the warner vs. Synchro in that car
Oh, and the warner synchos are a lot less expensive! Same are used in early z car 4 speeds.