Most flush cups are made of steel due to the stress that a sling point can put on them. Not sure if I would use a flush cup machined into aluminum. With this being 7075AL that could be a different case, but I wouldn't trust 6061.
I did an Instagram giveaway, and you had to add a stock and the fore end length to enter. So we have a good amount. I’m hoping Unknown Munitions can make a list up for it, I’m pretty slammed right now!