Aligning the Gantry - an easier way?
My gantry was off by a small amount, about a 0.6 mm gap on the left side when the gantry was all the way forward on the Z axis. I tried gently bending the gantry but the gap did not change much if any. I am not happy with bending things so I looked for a better, gentler method. Taking the "L" brackets off and aligning (bending) them seemed like the proper way but before that I tried an easier way: shimming.
I added a 0.5 mm shim between the gantry crossbar and the "L" bracket on the right side to even things out. It did, the gap on the left side is maybe 0.1 mm if anything, close enough to zero for now and for the amount of effort invested.
Yes, a shim that is the full width of where the "L" bracket screws to the gantry would be better and I will do that soon, making a longer shim with the three screw holes to align with the parts. Homing and calibrating the Core One didn't take long and if the print is skewed by 0.5 mm over the 220 mm travel I can probably live with that.
RE: Aligning the Gantry - an easier way?
As already stated in the response to your first copy of this post, shimming works, but is probably not the easiest way. It was one of the early approaches discussed here, back in April I believe.
I also disliked the idea of bending the L brackets in place, and bent them to exactly 90° before installing them when I built my kit. But having experienced how soft they are (you can easily bend them with your fingers), I no longer have any concerns with Prusa's suggested method of straightening the gantry in place, with the belts loose.