If you want to use a free floating hand guard, you have some options.
There are a few FF handguards that have a cutout on the top rail to support an A2 gas block. Depending on the brand, you may have to remove the barrel nut in order to use theirs. Some may use the standard barrel nut that's already there. You will have to remove the delta ring assembly.
The other option is to cut off the sight post and bayonet lug as mentioned above then remove the delta ring assembly and buy a FF handguard that uses the standard barrel nut. The new handguard should slide over the chopped off gas block so you won't have to remove it.
Another option is to cut off the A2 sight post and bayonet lug, use a tapered punch (NOT a pin punch or you will just break your punches) and hammer out the tapered pin holding the block in place. Yes, the pins are tapered so they can ONLY be removed in one particular direction. You can remove the barrel nut and delta ring assembly and install whatever brand handguard you like. You can buy a new low profile gas block that either clamps on or held in place by screws BUT that chopped off A2 gas block will be more secure due to the taped pin holding it in place. It'll save you $$ not having to buy a new one too.
If you decide to buy a new low profile gas block, you'll want a 0.750" one.
Here's a pic of someone's chopped down A2 gas block.