If it doesn't read "(X)M16-whatever PROPERTY OF US GOVT" on the receiver it AIN'T mil spec, no matter who makes it. [rolleyes] Eagle arms lowers have a partially milled sear area to prevent inserting a DIAS, but at least use standard pins. All current non-M16 lowers have some kind of sear block, and only a BM and some early sporters/semi receivers will accept a DIAS unmodified. Who cares?
FWIW I like my Eagles better than my Colts. YMMV