I suffer from the same condition. Can't help with heavy gun issue, but regarding the sights, have you thought of having shooting glasses made with your normal distance Rx in the non shooting lens and depending on your build, about a 39" focal point in the shooting lens. I know it sounds a bit weird, but it sure works for me. I can see the sights like I was 20 yrs old again. Might be worth checking out.
I take it you mean the right and left lenses are made to focus at different distances? I personally know when my eyes change so that right/left lenses don't focus equally at the same distance, I experience significant eye strain. I suspect this may be a personal matter. I do have an eye disability, so who knows, maybe that makes the eye strain issue different for me. But I personally couldn't make that set up work.
I've also tried bifocals with the tops focusing at distance, and the lowers focusing around 3ft or so. That works fine for the revolvers, but I'm finding it doesn't work for the rifle. I seem to hold my head too low, and see the rifle sights through the tops.
I've heard of some people having the bifocals reversed for shooting - lower section focusing at distance, and uppers focusing to see the sights. I'm intrigued. Seems like I could learn to hold my head lower and look through the tops for revolver shooting, and the rifle sights would be easy to see when I drop my head to nestle against the stock. Anyone actually use this set-up? Do you like it?
Also, I've seen what looks like a stick-on diopter that goes on the dominant eye lens for shooting. Almost looks like a rear peep sight stuck to the glasses with a suction cup. Anyone use that?
But I guess I'm straying from the original topic, which was guns for bad eyesight, not glasses for shooting. I love Mean Bob Mean's suggestion about open top conversions and pointability, since I've been looking for excuses to get a pair of them.