Putting a wategate off the exhaust housing can cause turbulence... you could drill it but it would take a long time as u'd have to use a small bit and drill about 30 holes to do the circle, also the manifold is split in the middle so 3 cylinders/runners per side, i'd mark it out and take it to a Fab or engineering shop and get them to oxy or gouge it out, also u'll need them to scallop the wastegate pipe that goes over the back of the manifold as it's not a circle it goes down the back a bit, buy the buttweld fittings from Bunnings should cost less than $15 for both...