Howdy and welcome, ODM27!!
If you want to keep your accuracy out to 400 yds.---- well I'll assume that you're shooting at targets that are at least big enough to see. And of course, you're dealing with SKS accuracy, not a rifle that might be more appropriate for long range shooting. Nothing wrong with that, just need to keep perspective.
Many of us here have done the scope thing with as good of success as is possible, and that would be my personal choice for an already modified SKS.
For long range targets without magnifying optics, I've always thought it would be great to find an aperture type front sight insert to use in conjunction with a rear peep sight. I'm talking a front sight insert with a hole in it so your target isn't obscured. And no, I've never seen one.
I'm very happy with my scoped version, but I would like to find a higher quality compact scope to use with it. jd