I guess with the one pictured there'd be nothing extending out under the sight/gas block like on the SL? Don't know now. Might look for something like NVhntr's suggestion...
Honestly if you want a longer handguard, I would just get rid of the A2 sight and install a longer free float handguard, low profile gas block, and a Magpul front sight to match the rear. A roughly 13" long handguard is a nice size for what you've got; it'll give more room for hand placement and a longer sight radius too.
That's a good opportunity to install an adjustable low profile gas block anyway, and tune your rifle for your ammo.