I just bought my first shotgun, i have owned rifles and handguns, fired many shotguns but never actually owned one, so i decided on ne of my long time favorites, the 870

i found an "Express Magnum" at a local gun store, in great condition with a brand new barrel, it has a "cantilever" optics mount, its great.. but i do not plan to use any sort of optics, so i have two questions
1. what is the best way to remove the mounting base? if it indeed can be, without a grinder, the screws had some sort of locking agent, which made it very difficult to remove the screws, the base itself seems to be "glued" on with epoxy of some sort, at least thats what i figure.. unless its welded on possibly?
2. i would like to use some sort of iron sights, the barrel is choked, so i dont think i can drill and tap for a bead sight on the front, i have seen the heat shields with "ghost ring" sights built in.. anyone have any sort of experience with them? or other suggestion for removable iron sights? i figured there would be something i could bolt to the cantilever mounting base, but i have been unable to find such a sight

thanks for any advice