The one circled red, not the one with the black arrow. I mistakenly undid it when removing the plastic cover after removing the starter motor. I am assuming it would be called Engine to Transfer case bolt but I cannot find a reference I am sure of in the manuals.

 
Hung like Einstein, smart as a horse.

https://www.swtc.edu/Ag_Power/diesel_engin...values.pdf

That�s not exactly a crucial bolt. I�ve been in the motor trade for 40+ years and I�ve never known a mechanic to torque bellhousing bolts up. Just tighten it up like a normal nut. Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.

Looks like a bell housing bolt. If you are not too sure of how tight to get it just do not use a long bar just a good everyday ring spanner, you could always add some locktite.

Another method would be to try and turn one of the other in the set as if tightening with a ring spanner, that will give you some idea how tight they go. Steve instinctively will know how far it can be pushed as I once would and not the sort of thing to be air gunned up. FL2 MY10 TD4 GS traded in at 2 years
FL2 MY13 TD4 GS Current

The bolt had blue colouration on it so looked like it had been locktited before. I think the torque for it is 65nm, so I put some locktite on it and decided to tighten it until my nerve went but the torque wrench clicked first.  
Hung like Einstein, smart as a horse.

I just tighten them until my elbow clicks!  Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.