I just finished modding my GoG Extcy to give it a milsim look. It would have been cheaper to buy a G-1 in the beginning but hind sight is 20/20 and with this I can still return it to stock.
In a couple of months I plan to run macroline up through the magazine and then down through the handle.
The mod was done with a SP-1 to G-1 conversion kit and a fake magwell. I had to dremel space for the regulator and dremel out a place for the eye covers. (I tried just putting the detents in with out the springs at first but the fit was so tight the detents where catching the bolt and causing it not to function properly. It took me about 3 hours to figure out it was the detents being in so tight that was causing it not to fire properly.
It's shooting like a champ now and feels really solid when I hold it.
Tools involved: Dremel, Drill, Tin Snips, Pocket Knife.
I wanted to change the handle to a black one but I don't want to spend $30 for a kit. I decided not to do the stock because I wanted to keep it as light as possible because I do like having my tank on my marker and the mobility that a speedball gun provides.
Edit: I have a shorter apex2 barrel that I will be putting on it and will give it a nice supressor/submachine gun look to it.