What’s your price point you are looking at for 556?It is a sign of OCD personality.
Most of my long guns are bought in matching pairs. One to shoot, one to keep so 2 to pass on. I almost never sell guns, and never if it breaks up the pair.
I broke the pair rule only ONCE when I traded Galil for MP5. MP5 package had everything I would have bought to keep it for ever. And it is going to Jordan, not a random ODTer.
To satisfy my OCD, I am already lookimg for the 5.56 Ace at a good price to pair up with a lonely x39 Ace.