I did weigh the ML frame with a 300g seatpost attached. It was right at 5 pounds. The fork pre-cut is 2.5.

I guess I am not getting this thing built this weekend. I guess I can have everything sitting on ready for the brake. I don't think I am going to get Lynskey to ship me a post mount adapter. I am just going to order a flat mount brake and be done with it. I'll add the other post mount brake to my spare parts bin.