Not intending to spoil your Gun Show experience, but INGO Advertiser Damage Industries is having a can't beat it sale on what you're looking for...
Upper Receiver, Stripped, 1913 Rail Top, USGI M4 | Damage Industries
AND, if what they're shipping is the same as the pic, Cerro Forge is top quality (look for the keyhole mark).
Awesome. Thanks for the tip!!