Yeah, that is how Colt and FN America assemble their rifles. They manufacture their precision parts and then haul em down to the local auto mechanic shop for assembly.
Now I grant you it isn't rocket science and the lower assembly is a piece of cake, but wait til you scratch the lower using a regular automotive punch to start/drive in the bolt stop lever small roll pin.
When I did my first AR lower build I was worried about that so I put some blue painters tape around the hole. turns out I didn't need it but it was great for peace of mind.