All your bitching and whining about parts quality and not one person actually helped this guy out. About selling the lower, that may not be a bad idea because the new Eagle Arms/Armalite/Cav Arms receivers are going for $95. Considering a grip costs $10, stock costs $35 minimum, plus the receiver for $100, you're already at a $40 disadvantage. If you can get what you paid for the lower, then by all means go for this. The Cav Arms parts kits run $60 and according to their site, they include all the parts required to finish the lower (which I am assuming includes the buffer spring and buffer, but I'd call and check about that). Now we're up to $155, maybe $170 if you include shipping and handling.
If we have $400, sold the receiver for $110, that'd give us $510. $510 - $170 = $340. For that much or maybe just a bit, you have a lot of option. 20" A4's from ADCO start at $375 and you'll know you'd be getting a high quality receiver. If you hang around the EE for a while, you might find somebody selling one with rear sights already mounted. That way you'd be ready to shoot right away rather than having to order sights.