#2 is the oil sender. I just checked on my 18RG and it's there, similar shape, with a wire coming out of it.
#3 is correct, it is your Number-2 Chain tensioner. Its sort of a long hex bolt looking thing with a screw or something like that that goes down it's centre.
#1 is okay to be blank 'cos your oil sender is already there (ie #2).
Shame it's EFI. A manly set of carbs would look very nice hanging off the side of that engine.