You WILL have to engrave your info since you are the maker of the NFA firearm. DoubleStar made the lower, yes, but you are making the NFA firearm by adding a SBR upper to it. The title of the Form 1 IS "Application to Make and Register a Firearm" and the lower will go into the ATF's records as a registered SBR now, with you as the maker.

You can always call them to double-check (304-616-4500), but I'm 99% sure on this one.