I have something similar to that. It started life as a Colt A2 upper I got from a friend. I put the barrel into a flattop upper receiver, and added Magpul MOE furniture, as you did.

It has a KAC 200-600 rear BUIS, and is very accurate. I use it to practice zeros and holds, for my other AR's that have a KAC rear BUIS. It's also a bunch of fun to shoot at distance.