Well, just since you asked.
1. You'll be spending $200 to officially announce the existence of this rare, obscure rifle (which might not appear on your state's "assault weapons" list, if your state has one) to the federal government. If the ATF suddenly decides that SBRs are now "prohibited" weapons, the way they tried to do with "arm braced" handguns, you're screwed.
2. You MIGHT discover the same type of problems that Colt had when they tried to make a "carbine" out of the AR-15/M16 when they simply hacked the barrel off right in front of the gas block/front sight base: not enough "dwell time" to the gas in the barrel ahead of the gas port to reliably operate the system. Again, I don't KNOW if this would happen, I'm just raising the possibility that it COULD happen.
3. If you DO have the problem in #2, you might discover that replacement barrels are not available today to fix it. I have no idea what the parts situation is with these guns.
4. The shorter barrel WILL be louder than it is now. Of course this can be mitigated with a modern suppressor (at the cost of another $200 tax stamp), but the resulting fix will probably be at least as long as the barrel is now.
I'm not familiar with the Korean Mission Adapted Railed Stock assembly. Can you post a pic of it? I'm willing to believe that this change MIGHT actually be a GOOD idea, assuming of course that you can actually get one. I'm no fan of the wire stock.