If you continue with right hand drill bits, you will get to the threads in the cylinder boss before it breaks loose. As the bit heats up the bolt, the bit direction will keep tightening it.
With left hand bits, the heat of the drilling will liquefy the Loctite and the bit direction will most of the time back out the bolt without resorting to the E-Z Out.
The tap, tap takes patience and light
taps to keep from deforming the bolt and locking it tighter as it deforms.
Bolt length is too critical to use for manifolds. A hair too long and they bottom out, too short and they don't grip enough thread depth. Add gasket crush thickness and you just don't know.
Have you ever had to torque down a long bolt through two pieces of metal while holding a backup on the wrench? Know how much harder it is turning that bolt than just torquing down the nut? You can't get a reliable torque reading turning a bolt rather than just the nut. The studs have their own torque rating.
Ace Hardware usually has automotive quality metric studs for the intake and exhaust but none long enough for the mounts. Expensive.