I'm looking to add a FF handguard to my SW mp15or. I'm looking to improve accuracy as well as have the option of rails to add acc. if wanted. Also I would like to get a more forward grip on the gun.

I've about decided on the vtac extreme ( I like the slots better than the holes) in either a 9 or 11" I'm kinda leaning toward the 11". What are your thoughts on the 9 versus 11" on a 16" carbine ?

The gas block with the rail will have to come off. I've heard some say these are a real PITA to get off the mp15. Anyone have any experience getting these off ?

Also I will need a LP gas block . What are your preferences to go under the vtac extreme with the least interference with the backing plates?

I personally think that a longer tube looks and works better on a 16".  I put the 13" Troy on my 16" and I love it.

Any advice on the gas block ?

Mine has a lightweight barrel with a .625" gas block section, so I don't have a frame of reference for how a standard gas block interacts with the tube, but if you use a standard generic lo-pro block like this, you should be fine.

I looked at that one . It's out of stock right now. I was also looking at the one from YHM.

They're all basically the same.  Take a look at Midway or Brownells, they usually have a few to choose from.

Find out if SW uses taper or roll pins, remove accordingly.  I have the 11" rail, it's awesome.  Any LP gas block will work fine, especially if you have a carbine length system and you're running an 11" rail; all your accessories will be forward of your gas block.