i bet 10 to 1 the Easy-out(tm) snaps.
left twist drill bits are ok. but are no panacea for this stud, IMHO.
the best tech. is getting perfect center and working out the drill size 1 at a time
using a numbered drill set. (dead center a must)
with manifold on the floor or in a vise.
keep working the size out , when you hit root size (look up metric size see tap size)
Machinist Metric ISO Screw Thread Tap - Drill Size Chart - Engineers Edge
those studs are put in extra tight and will be siezed ofter 100k mi.
( i suspect suz factory spot welds them in , but not sure
)
on 2 of mine, i did that and when i hit root, the stud was just a coil, i grabbed it and
it pealed out like a spring. saving the threads.
those Calmini headers will cost you.
one more trick is heating it (the stud) and then spraying your fav. penetrating oil it.
repeat 3 times, pray the vacuum created , sucks some in side.
but on mine no way Jose'
Ymmv..
I wouldnt give up until the header was cracked in half. LOL.
another tactic is to drill it and tap it to the next Metric or ISO USA inch standard thread.
which ever is smallest.
or
drill it to the HELicoil size that fits. (this will weaking the tiny mount)
dont forget you can sell the old header on ebay. ( and subsidise the new one)
id buy it.
cheers.