There's also a thread on ARFCOM about cutting the A2 front sight down to a low profile gas block. Dremel tool for the cutting, and you don't have to disassemble. This works well if you're covering it up with a tube or railed forend. In this thread the guy cut on an A2 front sight disassembled, but with a vice holding things steady, you could do this on the gun fairly easily. By the way, some older Bushmaster Modular carbines had milled A2 gas blocks under the railed forends.
http://www.ar15.com/forums/topic.html?b=3&f=4&t=226782
http://www.ar15.com/forums/topic.html?b=3&f=4&t=226782
