Turbo Fixing Hardware : Bolts and Studs

TL;DR Sisyphus's Caterham

Staring at the cover picture for the Lamba sensor blog post from the other day, I was surprised to discover that my turbo is missing a bolt that's supposed to keep it strongly attached to the cylinder head.

Browsing my photo gallery, I could confirm it was in place and partially visible with the turbo fresh from its upgrade in January. I could also spot a closeup of the turbo from the blue factory demonstrator that showed there's a bolt where mine seems to be missing (see below). 

Videos of of the R06A teardown mentioned here show that the Alto Works uses 2 bolts and 2 studs.

I really lost one bolt then. The good thing is that I have no exhaust leak, no noise or traces of soot. Overall it's not a big deal : I'd rather lose a bolt than risk ripping the thread in the aluminium cylinder head.

Looking for a spare, I mostly found M8 and M10 studs and nuts kits. I confirmed the size with an M8 nut I have in my drawer. As it threaded fine on the top-right stud on the car, M8 it is. I got a set of 4 stainless-steel studs and nuts from Amazon (again) and plan to use some copper grease as an anti-seize to prevent galling.

"Why that mix of bolts and studs ?" we were wondering with Guillaume. My best guess is that it's just easier to align the turbo that way. The diagram shows that there is a gasket between the head and turbo inlet, confirming that it's most likely to help with alignment.

How tight should I torque those ?  The service manual states 33 Nm, I should probably lower that to 25 Nm (-25% or so) if I use a lubricant on the threads.

While the studs on the car have Torx head to set them in place, the ones I found are just bare thread on both sides.

What's the best way to tighten a stud with no dedicated feature to do so ? I've found tools to remove studs, but not to install them. I guess I'll use the old trick of using a pair of nuts that I'll smash into one another, then torque the stud in the cylinder head with that.

EDIT after the work : Shorter thread of the stud went in the cylinder head to retain enough thread on the outside (yup, I had to reverse it...).
Overall it was really difficult to get any tool on without removing the exhaust system from the turbo. The only thing that worked were regular and ratcheting spanners. Torque is thus very approximate and limited by the short lever they provide. Serrated flange nuts from the kit have 12mm heads (wtf) and are a bit slim to my taste. I could see thicker hardware and wire-locking for good measure.
The fastener I lost was a drilled allen bolt with a lockwire used as an engine seal : once the turbo or valve cover have been removed, the factory can tell the engine has been tempered with.
This is why I did wait for the car to be out of the 2 years manufacturer warranty period as well as close to the end of the garage's (mandatory) 1 year warranty before having it souped-up a bit.