The front sight will have to be mounted on the gas block. The rear sights will sit as far back as possible on the rail.
Will they be two different heights or will they match up?
Any ideas which set I should go with.....they dont necessarilly have to be a set. Meaning I can get one from YHM and other from Troy.....that really doesnt matter. AS long as they are in line of sight with the other.

What brands do ya'll recommend?

Well i asked the same question a while back before buying my sights and everyone recommended Troy Industries, So i bought a diamondhead Folding BUIS haven't tested it out yet but i can tell you it's durable, and very well crafted, i would recommend getting a set of troys but in the end it's your money your decision, as for lining up if you had a FSB with an F marked on it they should line up no problem but since you have a gas block and your mounting the sight on that I couldn't tell you, odds are they probably will line up but i don't know too much info about that and i wouldn't want to promise you something and have it turn out to be wrong.

-Dep