I have a DPMS detachable rear sight...  It has the "A2" rear sight assembly in it with the 1MOA adjustment, marked 8/3.  The useable elevation adjustment for it is only 600 yards, as it stops at the 6 anyway.

I would really like to have the A3 1/2 MOA sight assembly with the 6/3 elevation wheel.  The range I shoot at has 300 yard, 360 yard and 500 yard steel sillouette targets, and I can tell a difference in the accuracy dept when dialing in with my shooting buddy's RRA Tac handle compared to mine.

Would it be possible to purchase the A3 rear assy from some place like Bushmaster and swap rear assemblies, or is the DPMS somehow more permanently attached or using some additional proprietary mounting procedure? (There seems to be an additional roll pin under the small aperture.

I really like the DPMS detachable itself, as it's noticeably lighter than a chopped CH, and the screws are on the right side of the mount, which is completely backwards, but perfect for a lefty such as myself.

Thanks for your time.

Standard elevation wheel, you can change it out with a 6/3. The one I had came with an NM wheel.
Be careful though, that sight has a reputation for breaking the mounting, cross pins.