Do the holes line up? well yes and no ::). The hole that the grip screw goes through lines up but you will need to make another hole for what I am pretty sure is the hammer strut. Why Umarex extended the hammer strut through he grip I'm not quit sure but there it is. You can see in the photo ( sorry about the focus) the top hole is where the hammer strut come through and the bottom is the grip screw. I havent changed the grip on the HK since I like it but I have changed one out on my Colt. The stock is easy to replace and you just need to get a mil-spec sized stock to slip on. Here is the HK with a Magpul I slipped on for the photo.
Hello, There are a couple things that make the aluminum guard a little difficult to make work. Yes the holes dont line up just right and the front of the guard extends slightly into the mag well and needs to be ground down. The plastic ones works great and are much easier to make fit.