Auto zone has the diagrams on line if you go to
www.autozone.com
Then on the left side click Repair Info then click Vehicle repair guides also on left side then cilck on Driveability & emissions controls in the center of the page then click on Vaccum diagrams at the bottom on the right side.
Then scroll about half way down and you'll see '84 305 auto and manual trans.
im not shure how you will determin what diagram will be effictive for that truck.
I tired to link to it but it didn't work sorry.
hope this helps
Good luck