You have quite a bit to choose from. First Id make sure it would fit under the rail -- which I think most low pro's would. Then choose one that uses set screws from the bottom to mount onto the dimple. Personally, Id get it pinned on top of that. Not that big an issue if not even atleast partially exposed though I think. -- I could be wrong.
As for brands you have the better known and I suppose old reliable ones like Vltor, KAC, and well... Larue.
You dont have to send it off IMHO... Once youve mounted the rear set screw on the dimple and verified that gas port alignment is GTG, you can use the hole for the front screw as a guide to drill your own dimple for it.