This Yankee Hill Machine Low Profile Gas Block With Pinch Screw Mounting features a straight cut located at the 6-oclock position on the gas block.
This would not likely fit inside the Daniel Defense MFR XS handguard.
Yes, this will fit inside of that handguard.
Yes, it is for barrels with a .750" diameter at the gas port.
It depends on the gas journal diameter of your barrel. This gas block has a bore diameter of .750" which is the most common size for M4 barrels.