The thread for the 1 in monarch forks to gt2a frame is one below this one i believe . I used 1 in copper and couplings. There is no slack in this when done right. The only thing that might happen is possibaly the copper might wear because its softer then steel. Sort of like an oilite bushing which is bronze . But its what you want to wear and simpily replace. Now i dont have any mileage on this bike so i will update how it holds up after some time.
What ive learned is the headset on the gt2as frames is whats called a "zero stack" and takes 1 1/8 bearings. There are a few versions but not what is needed to use a 1in threaded steartube in these frames
http://www.canecreek.com/tech-center/headsets/shis/overview
So any forks set up for this type of headset should work. I remember reading when i bought my frame two years ago they were saying this frame uses "standard mountain bike " parts. So i would assume any suspension fork from a newer mountain bike should work, but dont blame me when they dont, just passing on what i read. I do know a lot of mountain bike frames now use a threadless stear tube fork. So there is a version of the monarch whice uses the threadless set up and that is what kc used recently on his build with out an issue.
Hope that helps lol , i like you searched and searched , even hit the local shop and he even seem a little confused as to what i had .