I did one of these a while back , went with the Ati mount as you mentioned, it did require a bit of screwing around to get lined up with the bore and a bit of loctite to hold it on as the previous poster mentioned, once on all good, i like it sits still, seems rigid, tried a couple different scopes, It ended up with a Jager 6-24x50 ( german tasco ?) liked that ok as well, but any decent scope 4x would work fine on this gun.
but after a hundred or so uncomfortably shot rounds i realized the best thing you can do to help this rifle is throw the heavy odd angled, fencepost type stock it is mounted on in the fire, i went back to ATI found a decent composite aftermarket stock for it, knocked a bit of weight off it, made it way funner to shoot, more comfortable and there for more consistant in the accuracy department, and imo a LOT nicer to look at........ while it may not shoot moa or anything it does shoot minute of white tail 0-300. Mine still had a long untouched barrel, complete with the lugs to mount a bayonette on, when i got the rifle the barrell was packed full of some sort of waxy grease, so i assumed it was probably surplus unfired, it still had nice sharp looking rifling etc. I like mine it is not tack driver but will make them jump in the deep freeze no prob. enjoy your rifle.