Installing a set of hidden tailgate latches on my "55. Is there a preferred placement besides towards the top and does the latch mount on the tailgate or the bedside? It would appear the latch should go on the bedside to get more clamping power. As far as overall placment I believe right below below the top rollover seam on the inside of the tailgate.

 

are you using just the latches or do you have the tailgate latch kit ???
my new bed kit with the hidden latch tailgate came with a templete with instrustions had to use the templete to get it right i can give you some pictures if you want

 

You've got it all figured out. Latch on the bedside and catch on the gate. Place it as high on the sides/gate as practical.