I ran into the same problem, and called Harlan. He and Steve? said that the rear trunnion holes on the receiver had to be elongated forward to let the trunnion take up the gap. I did, and it worked.
Another thing I noticed with the NDS-3 is that the gap between the selector and the top cover is wider than when using a OOW receiver. Hmmmm.
dont know about the folders.......
but man i just did 4 of the NDS style and they were perfect in every way.
say what you mean & mean what you say
There were a couple of other good ideas too but the above was the easiest.
Do you really think the problem is in the receiver? I've built several from NDS and never had that problem (I have had some problems that I caused myself, however)