The Chilton manual makes for mighty fine campfire kindling - especially when it comes to the Sidekick!
I am not aware of any vacuum lines that go from the "back of the cylinder head" to the transmission.
I am not familiar with the 5-speed ( I have automatics) so I cannot say for certain that there is a breather hose on the manual transmission. If there is, the other end would terminate with some sort of breather cap (ie. not connected to anything) in a higher location probably in the engine compartment attached to the firewall. Perhaps that is what Chilton means when they describe "breather hoses from the back of the cylinder head" Plural "breather hoses" may also include a breather hose for the transfer case.
I hope that this helps!