If the extension is permanently attached, I would have it engraved first. Not sure if you are supposed to have it engraved before sending the form to the ATF.
The Trust info is around here somewhere and I haven't gotten my receiver back yet so I'm not that far. But Mario at POHF and Orion Arms are good suggestions for engravers.
The Trust info is around here somewhere and I haven't gotten my receiver back yet so I'm not that far. But Mario at POHF and Orion Arms are good suggestions for engravers.