Gibbz has a rather unique method for mounting their handguards. First there is a Base Mount that threads into the upper and you slide an internal castle nut to secure the barrel to the upper. After that you slide the upper onto the Base Mount and secure it with 4 button head screws. Makes it very simple to remove the handguard if you want to add some rails to it. Those long narrow slots are the mounting points and it's a hex shaped handguard. So, you have the top rail, provisions for adding rails or rail sections for the full length of the bottom and at forward and rear positions on the upper angled surfaces on either side of the top rail.

As for the upper, it's a side charging upper and Gibbz offer them in right or left handed and with options in terms ejection port size, ports covered or not, and bolt assist or not. They also offer uppers for AR-15 or AR-10 caliber setups. Plus they offer a variety of Cerakote colors or patterns. Downside is that these parts are NOT cheap but when you are building a full on custom you have to expect it will be rather spendy. This rifle was a present to myself as a reward for going a full year without cigarettes. BTW at present I am 6 years smoke free.