I’ve done the same: ATI conversion to one M-N and original restoration of the second. On the ATI conversion the barrel floated high until I put in the washer on the rear receiver bolt, which fixed that problem. I also had problems feeding stripper clips and then getting the bolt to eject properly. I had to take quite a bit of material off the inside of the ATI stock, right at the ejector bar, to give enough clearance for it to work properly. Now both guns work great and the 7.62X54 is a lot of fun to shoot but I’m no longer as satisfied with the .223 AR-15 and wanted a higher caliber semi-auto, so I had to purchase a M1-A (so I ended up spending a lot more than I set out to for my inexpensive rifle).
I’ll drop in that rear washer tonight and see how much it helps.