I hadn’t looked in the books (yet), but at first glance, it looks like a /6 to me.
The red arrow points up, for all the exhaust tubing I have ever seen had the bolt located on top of the pipe.
For a /6, this would point the other end towards the front of engine.
If it was on a small block, the other end would either occupy the same space as the transmission bellhousing (if on passenger side) or the frame rail (if on driver’s side).
There is a small possibly it might be for a big block for there are so few of them that I’ve seen with an A.I.R. pump or aspirator (in my area) for me to recall what they looked like.
I hope this helps.
BudW