Getting the gas block bolts out isn't the issue -- that can be done with your 'L-shaped' Allen wrench. Just go slowly, backing the bolts out 1/4 turn, tightening back down 1/8 turn until they're out. This will help keep the staked part of the bolt from boogering up the threads in the top half of the gas block.
As for torquing the new bolts, you're gonna need either a 1/4" drive, 9/64" Allen socket (like
this one), or a 9/64" Allen bit (hex on the back end) with a 1/4" drive-to-hex-bit adapter. You'll probably also need at least a 2" extension to give you enough room to work.
Be sure your torque wrench reads in
INCH-lbs., and that it will adjust to 30-35 in-lbs.