Not sure exactly what its for, but in replacing my timing belt and retiming my 2.3 (Holley 5200 V2 carb), I also investigated the vacuum lines- I have a similar one in my Bobcat wagon, and it was routed to the manifold vacuum that comes from the intake- it has a three way, one line coming from a round valve on the air cleaner which tees and goes to the intake manifold, one going to the dashpot, and one going to the vacuum canister in the drivers side wheel well. (See pics) I do know that it took some experimenting with the vacuum lines to figure out which routing of it seems to make the car run the best, but after changing things around for a couple of days and watching different thing like how long it would take to warm up, the time it took to kick down, and what the gas consumption seemed to be, this was the best routing to me- hope it helps!