[Theisey]

Maybe this will help.
The references to "his line" or "the line" are actually two different things.

In (a), his line is the line of scrimmage. So you can hand the ball forward to the snapper, either guard or either tackle if we talk standard balanced formation if he does the 180 and is 1 yard behind the LOS.

In part (b), as long as the player was the END on the line of scrimmage you could hand it forward to him without those additional restrictions of a 180 and being 1 yard behind.
The restrictions in (b) are you can't hand it forward if you are on the end of the line and are the snapper or as it says, adjacent to the snapper who is on the end of the line.

So, if you had an unbalanced formation such as this:

• b.0 LE rT LT LG S rG rE

you could hand it forward to the rE without any of (a) stuff.
But if you had a formation such as

• b.1 LE rT LT rG LG S rE or
• b.2 LE rE rT LT rG LG S

you cannot had it forward to the rE in b.1 or the S in b.2 without complying with the stuff in (a)