The interference could be the lock and barrel at this point. The lock bolster may need tapering at the rear to get it flat to the barrel. Just make sure to keep the bolster surface flat from end to end. you are getting into the last .010"-.020" of final fitting, so go really slow, and be certain you are hitting the problem spots. Filing in one spot may make a high spot somewhere else. I'm not familiar enough with that lock to guess if there may be metal to metal interference somewhere else too.
as for tired eyes, really good light (more than one usually), and as much 'correction' as I can create is always a good thing for me. I have trouble with 'visors' with only one focal-length lens, and find them too awkward too.
I've started stacking reading glasses, one behind the other to create a 'bi-focal' setup. Two 2.75x sets (for me), with one set being half lens height of the other. I can look through the single set on the top half to see the workbench and tools, then look through the lower (both sets) to look at the detail work at about a 6-8" focal length. Takes a bit to get used to, but without it I may as well be working in the dark. Im sure I look a bit strange, but ain't nobody looking at me in the shop except the dog. As long as he gets fed and gets to go outside a few times, he don't say much.