The offset for a gas block, if your gas block needs one, is .030, not .003. It is the thickness of the handguard cap that sat between the fsb and shoulder of the barrel, to hold the front of the OEM handguards.
Many gas blocks do not need to be offset .030 because the manufacturers realize you are not going to install OEM handguards. As stated above one of the holes for the set screws will line up with the port hole in the gas block. (That is how they machine the port hole in the gas block) Flip the gas block upside down and see if you need the .030 offset or not.
ETA: A carbine lower should not make a difference as carbine buffers, even the heavier ones, are lighter than the rifle buffer.
