Your Dad making the lower for you is technically a no-no. A gun can be made by an individual for their personal use, not for the intention of being transferred. Could he machine it, you visit and get it from him, and you both keep your mouths shut about who built it? Maybe, but I wouldn't risk it (being a chicken). In the name of heaven, *do not* have him mail a completed receiver to you. Only an ffl can receive a gun, which is what that finished receiver would be. Very, very bad juju for you if you get caught. The ATF never takes a "boys will be boys" stance on those sorts of things. Better to visit Dad and spend time with him & let him help you finish the receiver.
Build a gun, enjoy it for a while, and it *can* be sold or given, but it has to be marked with the builder's name, city, and state. Here's a couple links to scans of an ATF letter stating it:
(sorry about undoubtedly screwing up the link insertion...)