is there any legal issues (or rules that apply)to making and selling incomplete side plates for a MAG 58?
I am not familiar with the MAG 58 is the side plate considered the registered part?
If the side plate is the registered part I believe you can do it to 80% but no more. If it is not the registered part then it could be completed.
You should check with the BATFE they can be found online, just google it.