Based on my limited research on the 586 a used one sells for atleast $500 and they go up from there. Trading the 586 for an SKS is a bad deal in my opinion. Also originally SKS' came with 10 round fixed magazines so more than likely the magazine well had to be modified slightly in order for the 30 round magazine to fit. It's a very bad trade in my opinion.
I would suggest you keep the 586, and again based on my limited research they're becoming harder to find so its value will increase over time.
"It's a gun you loaded on Sunday, and shot all week."
"If God didn't create man equal then Sam Colt had made them equal."
"Fast is fine, but accuracy is everything."