I have a new pro picks box and new chains but I can't figure out how to install the chains see the pic attached and let me know your thoughts

 

Hi,

that's how it looks on my '56 (I think, that's stock):

I'd say that You'll have to mount the latch at the back side as well, otherwise
the latch is too long and you wont get enough pressure to keep the gate shut firmly. So in my opinion - mount the latch on the back of the end post,
sticking the bolts trought the post (as you can see on my truck). Before boring the holes, you can shove the latch outward until the shackle can be opened easy but with still enough pressure. Maybe the end of the latch will
overlap the end post to the side, but that's no problem...

 

Here's my latch, northern classics installed it

 

My latch maybe different