You have a rifle length+1" gas port? Note that some handguards that advertise 13" are actually 12.65" (like your current).
I have semi-bad news for you. From your picture it looks like, if you want to change handguards, you might have to remove that gas block in most cases. If you happen to pick another handguard that uses the exact same barrel nut as the current one, then you might be able to avoid it if you cut off the sling attachment and mill down the bayonet lug. But handguard barrel nuts tend to be proprietary, so good luck on that.
Removing that gas block could be a little tricky as I have found the blocks pinned like that, really take a lot of banging to drive the pins out and you need the right punches. In most cases the pins are slightly conical, so they only drive out in one direction. Looks like there are already some idiot marks around the gas block pins, reflecting either lack of skill on installation or someone trying to remove it in the past.
Once you remove the gas block, it also gives you the choice to replace it, which you can do with a lowpro, or you can cut of the sling attachment and mill down the bayonet lug, and possibly turn it into a low pro. If you go with a new lowpro, then you might need to get a compression block rather than a set screw, since I am not sure where the set screw would line up with the slots cut for the block you have. If you get a lowpro or cut the one you have down to fit, then it will open it up to a 13"-15" handguard.