They can consider any serialized part a firearm if they wish. They are the .gov... you are not.
The general gun population will not send parts to any tomdickharry who offers a service. I sure wouldn't trust anyone without an FFL, liability insurance, business .....
I could make a list of a bunch of guns i have, or "have", or wish I had. Why would one feel compelled to provide that infornation freely? Do you feel the need to show off? Is it some immature game of oneupsmanship?
Why do you feel it necessary to list your guns?