You shouldn't have to seperate the receiver halves to get it engraved.
I had mine laser engraved just above the pistol grip on the right side where there is a narrow flat strip. The text height and depth is to batf requirement, but it's barely noticeable, which is how I wanted it.
I stripped mine down as much as I easily could: field strip and sights.
Call your engraver, explain what you need done and hammer out the details with them. Iirc, it took about 3 days and cost about $50.