I actually prefere the clamp on types of gas block over the pin on and set screw.
The pin on types have not a lot to keep them from being knocked crooked. If they werent so darn tight we'd see more of that. But for what they are they work well.
The set screw type need a jig block bolted on so you can drill dimples into your barrel that will locate the gas block. I use these for low pro gas bocks only, not sighted blocks because its easy to drill wrong and screw it up.
The clamp on types can be very tough. I put them on with CLP oil and shot my gun to make sure it works. Then I mark the gas block and barrel with a sharpie, punch, or awl scratch. Then I remove the block if needed or just loosen it and coat the inside edge of the block with red Permatex thread lock. And use red permatex on the bolt threads. Plus since they clamp on, as long as thier tight they aren't going anywhere.
Anything that can knock a properly installed clamp on crooked, probally would have damaged the sight anyway.
The red threadlock is really good at glueing metal parts together and keeping them from vibrating apart. Red Surelock is better at filling gaps between metal than red Permatex threadlock.
I think Knights Armament, KAC makes a gas block/ flip front site combo your looking for. The Magpul guys used it (I think) in there Art of the Tactical Carbine 1 DVD. They used rails behind it, but i think it was still the type that accepts M4 hand gards. I see If I can find a linky.
KAC has some bada$$ stuff:
Unfortuneatly this model is not on KACs website yet. And given that the AR evolution has gone allmost totally to rifle length handgards on carbines, I'm not sure it would be wise to produce. Most KISS and lite builds use a standard front sight.