Decimator/DecimatAR with OEM barrel

I have been incapable of finishing a decimator build with an OEM barrel; 2 different OEM barrels as a matter of fact.

I've reprinted the upper twice (once because I wasn't sure if I just really messed up the print, once for stripping barrel nut threads) and I've reprinted the barrel nut 3-4 times at this point.

I started this build just before fosscad was nuked, and since the Ark is back up (https://forum.guncadindex.com/c/ark@fosscad.io), I was able to see that there are threads where others have had this issue.

Has anyone overcome this issue personally? The build looks great and I love the AR fcg but I'm hitting a wall here. Should I just drill and pin the barrel nut with a couple of set screws?