I forgot to note, aluminium thickness next to the spark plug tubes is only about 8-10mm and I don't have bottoming taps - so I drilled right through, and the bolts have ultra-grey sealant on them to ensure nothing leaks out + the bolt stays put. All the other bolts have Toyota thread locker.
@JHZ I used aluminium crush washers under the AN fittings, plus I used an anaerobic PTFE sealant (Aeroflow) on the threads. Its oil/fuel/waterproof and is rated to much higher temps than the engine will reach. I'm sure it wont leak!