If you going to chop a section out of your buttstock, I'd suggest you drill a good-size diameter hole going fore-and-aft in the buttstock, that goes beyond ( more forward ) then front cut. That way, once the piece is removed, you can place a dowel in the hole to tie together the two pieces, add strength, glue, then taper the two sectons to the new contour. Maybe even two holes, one on top of the other, as far apart as will work out??
I'm not saying to do it, but if you do, I thnk the above will help.
As far a shortening the barrel, it's no big deal at all. A new cut and crown job may add accuracy, depending on existing condition. Probably easiest to put on a new, sporter type front sight, rather then try to remove and reuse existing one.