The quickest and easiest way to eliminate that A2 sight base is to simply chop it off w/ a dremel tool. Look at bushmasters "optics ready" carbines or the remington R-15's. That's basically what they have. Pretty simple task, chop it off, reshape the gas block portion with a grinding stone on a dremel, touch up w/ some flat, black Krylon and you're in business.
They are pretty simple to remove and replace, just remember drive your pins out from left to right. Use a 2# hammer and a good solid punch, getting them started can take a few good whacks.
I have no experience w/ the adjustables, but believe they are primary use in the bigger bore (pistol cartridge) AR-15's.
