Jefe,,, if slide mount is out of the question,,, I am not sure how else you would mount a red dot sight on a 1911 without drilling and tapping or send it out for the work to be done.
As far as not being able to focus, the rear sight, the front sight and the target are all in different planes. focus on the front sight, the target should be blurr and the rear sight should be visible enough to center and align the front sight. I don't know of anyone who can see clearly all. but a red dot mounted sight will certainly allow you to concentrate on the target since the dot just needs to be on top of it
As far as not being able to focus, the rear sight, the front sight and the target are all in different planes. focus on the front sight, the target should be blurr and the rear sight should be visible enough to center and align the front sight. I don't know of anyone who can see clearly all. but a red dot mounted sight will certainly allow you to concentrate on the target since the dot just needs to be on top of it