I would have a hard breaking up a pre-ban R6830 myself. Unlike most other models, they actually seem to be worth more as a complete weapon than as the sum of their parts. I personally have one complete R6830 and one R6830 lower receiver assembly that I got for a pretty good damn price because while they are functionally identical to any other Colt lower, that "7.62x39" marking seems to dim their value compared to the others in the eyes of most potential buyers. There really aren't that many R6830s in existance, either. They were only made for a couple of years and could have some collector value one day. I doubt a mix-master gun ever will.
Have you even fired the R6830 yet? It's actually a pretty fun gun and caliber to shoot in it's own right. I thoroughly enjoy the accuracy and punch the combination provides. The only Achilles heel of the gun is finding high capacity magazines for it. My collection won't ever be with an R6830 again.
My two cents, do what you want with the gun, but don't do anything irreversible and keep the original parts so you can restore the gun to it's original condition should you ever desire to. An upper receiver assembly doesn't take up that much room. That all being said, if you are still looking to offload the upper, I may be interested in a trade or possible outright purchase. I'm eventually planning on converting my R6830 lower receiver assembly into an M4-gery or possibly fit it with a belt fed Shrike upper should they ever become available, but I wouldn't mind having all the pieces to make it a complete R6830 as well. What are you lokking for in trade?