Raf- thanks bud. I really appreciate your help with this!
Josh- I used a heat gun on the low setting so I didn't over heat or burn the plastic. Heat it till it starts to get a gloss to it. Then for most of them, I used a cone shaped grinding bit for my dremel. This bit worked well in my opinion because it gave the dents a little texture. You have to be very careful to support the plate from the back side so you don't warp the plate and get only the desired dent. I tried a couple different methods, but ultimately put on some thick leather gloves so I didn't burn my fingers and just used my hands. For the large square dent on the left chest plate, I used a metal architectural scale, but I'm sure you could use flat head screw driver. I just looked for something to give me a defined line within the dent. Just take your time. You might have to reheat the area a couple times to get the desired result. Hope this helps.