I have a couple of  GT 1.6's and the bolt carier fits but doesn't slide all the way back.
Also it's obviously a much tighter fit due to the thicker rails, but there isn't enough metal on the bolt carrier to relieve it there, and I don't see how you could evenly reomove metal from the bottom/inside of the rail. I don't want to fit and polish these because I might sell them, this would be my first and I'm handy but these look hard to do. It does look like it could be fitted but then they are mine forever...
They are pinched a bit in the back, but I called GT and they said it would work(Iread them the measurements)
So has anybody built on one of these?