As a rule, the AIM only lists other engines if there is a difference. In other words, the L35 is the "base" big block for the 68 Camaro, therefore that's the one used as the reference. Unless there's a difference between the L35 and the L34 or L78 (or L89), the notes will say "L35". If there's no difference, then you can use the "L35" reference for the other big block engines as well.
The oil line references you see are for small blocks AND big blocks, with the small block connection being next to the distributor and the big block connection being above the oil filter. The bracket you reference for "belonging to L35" is also used on the L34 and L78 (and L89). But like I said above, USUALLY if there's no difference between the part used on the L35, there won't be a further reference to other big blocks. Exceptions to that rule are scattered throughout the book, I.E. look at item number 4 on that same page. Even though the L34 used the same part, they only show the "L35. 78".
I'm not familiar with what the 69 had, but yes, the 68 big block was a 3 piece arrangement with the number 5 elbow being used because of the close proximity of the oil line to the clutch Z-Bar. Even though it wasn't needed on automatic transmission cars, I would assume it was used anyway since the AIM doesn't state if it's for manual transmissions only.
You are correct, item number 11 is the Sender for the Water Temperature Gauge connection. It's drawn for the small block location.