The Steyr Barrels Are the Best by far ! Hammer forged and Accurate ! Yes the lower is Metric, and if that is a Steyr Barrel it should be Metric as well but lots of parts interchange, But mainly the Magazines are different, Is Your bolt Slotted with "Sand Cuts" or just Smooth ?
Tapco may still Have the Stock Set like I have with the Hook In it .They have some Regular ones too.
http://www.tapco.com/product_list.asp?dept=121&last=115
If you are interested!
Rich