Can you do engraving on NFA lowers?
Not usually. My laser is an older one without auto-focus, so if the part is flat I can probably do it. I do a lot of barrels for several gunsmiths around here, but I use the old pantograph and diamond engrave them.

I did put a Navy logo on a sideplate of a j-frame the other day for a friend. I used my new computer controlled engraver.

A little known fact I found out about several years ago; The ATF considers engraving as gunsmithing. Therefore, if a trophy shop keeps a firearm or receiver overnight, they are technically supposed to have an FFL. True or not, I don't keep anybody's gun overnight except my own.