I reckon if you went over it with a Stanley knife blade as I mentioned earlier, you could smooth those curves out nicely.Due to the alignment differences from the differing shapes I can't have this quite as tidy as I'd like - I'd probably need to get a fresh cut made of the original pickguard, but I'm not sure I care quite that much on this guitar.
What I would do is, screw it down to a bit of scrap timber or your bench so it's stable with the horn overhanging the edge. The hold the blade on the same angle as the existing bevel, drawing the blade toward you holding it with two hands for good control. Think of it as a plane. You should get nice little curls of material coming off the blade. You can also do it pushing away, but with a curve like that horn, I think drawing would be better, working from the neck pocket down.
As a side note, there is a good chance you could turn that Samick into a real player. The Samick factory made guitars for Fender in their Squier range in the late 80's - early 90's (and I think some Fender FSR models). It should have "good bones" and with new electronics, pickups and a fret job, there's heaps of potential there.
One of my oldest and best playing strats is a MIC 2002 Squier Bullet!. I've put stupid amounts of time & money into it with pickups, hardware and a refret and a refinish; but the neck just feels and plays great and it always sounds fantastic.