Although the 1761 is a new Anschutz model, having been available since last year, there aren't many threads about them. At the same time there are even fewer threads about problems with the model. It's possible that like every new model -- even the much-lauded Vudoo -- the 1761 has some teething problems.
Regarding issues with 54 sporters or match rifles, there aren't many shooters who report problems with them -- and it's on forums such as these where they are so often made public. And certainly big problems are rare. Some shooters put custom barrels on most rifles they own. But it's not an exaggeration to say that among factory barrels, Anschutz tubes are among the best. Of course, there may be the very few that are substandard.
With regard to the OP's problems, I've never seen a 1761. I'm imagining that when tightened past a certain point his rear action screw begins to protrude into the bolt raceway. If that is the case, he might wish to consider if his rear action screw might not interfere with the bolt if it were shortened a bit. Alternatively, he might consider a shim for the rear action screw under the trigger guard.
About the magazine and accuracy, it would be strange if a rifle consistently shot the first two shots errantly and the others in the magazine grouped consistently. Does the OP confirm that it happens all the time? Magazine ammo accuracy can be affected if the magazine is causing rounds to load improperly in such a way that lead is shaved off the bullet itself on its way into the chamber. Try loading a few first rounds and see if this is the case. Alternatively, try single loading without the magazine. Once properly in the chamber it should be irrelevant whether the magazine is in place.
In addition, it's useful to keep in mind that just because a rifle says Anschutz on it doesn't mean that it will shoot all ammo equally well. Fliers and errant shots happen most often with this rifle -- or any other good one, even with a custom barrel -- when the ammo isn't up to the job. No rifle will outshoot the ammo it's given.
About the quickness of a response from Anschutz, or lack thereof, keep in mind that problems such as these must be very difficult to diagnose through a third party query, even if it is from a small Canadian dealer.
Can some pictures be posted of the suspected problem areas?