I actually like the chest vents on the 1/100 Astray better than the PG's, so I customized something similar for the Ronin. The pics should say it all.
The "difficulty' I had with this mod is that stock vents didn't offer anything in terms of a guide, since it's totally different from the NG version's vents. So, i had to build the vents separately from the socket/adapter that will connect them vents to the chest frame. I later did a dry fit and made necessarily size adjustments.
I realized I actually get more work done when I do certain sections at a time instead of trying to finish one section in a go (when I get OC, I tend to spend a lot more time THINKING of how to do certain things than actually doing them, especially when the build is actually more complicated that i have planned it one paper). As I'm doing one part, I'm already thinking on how to do the other (don't ask me how i do it, even I don't know).